Automated laser workstation for high precision surgical and industrial interventions

ABSTRACT

A method and system is described that greatly improves the safety and efficacy of ophthalmic laser surgery. The method and system are applicable to precise operations on a target subject to movement during the procedure. The system may comprise the following elements: (1) a user interface, (2) an imaging system, which may include a surgical microscope, (3) an automated tracking system that can follow the movements of an eye, (4) a laser, (5) a diagnostic system, and (6) a fast reliable safety means, for automatically interrupting the laser firing.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation application of and claims thebenefit of priority from U.S. patent application Ser. No. 09/543,840filed Apr. 5, 2000, now U.S. Pat. No. 6,726,680 which is a divisional ofU.S. patent application Ser. No. 08/ 523,738 filed Sep. 5, 1995 (nowU.S. Pat. No. 6,099,522), which is a continuation of Ser. No. 07/843,374filed Feb. 27, 1992 (now abandoned), which is a continuation-in-part ofSer. No. 07/307,315 filed Feb. 6, 1989 (now U.S. Pat. No. 5,098,426) anda continuation-in-part of Ser. No. 07/475,657 filed Feb. 6, 1990 (nowabandoned), the full disclosures of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The invention relates to methods and apparatus for performing preciselaser interventions, and in particular those interventions relevant toimproved methods and apparatus for precision laser surgery. In onepreferred embodiment, the system of the invention is used for effectingprecise laser eye surgery. In other embodiments the invention isapplicable to non-surgical diagnostic procedures or non-medicalprocedures involving precision laser operations, such as industrialprocesses.

When performing laser interventions, whether in medical surgery,industrial processes, or otherwise, several fundamental considerationsare common to most applications and will influence the viability andeffectiveness of the invention. To influence the outcome of theintervention, the present invention addresses both the technicalinnovations involved in an apparatus to facilitate precision laserinterventions, and the methods by which a user of such apparatus canachieve a precise result.

The present invention addresses the following considerations: (1) howdoes the user identify a target for the laser intervention, (2) how doesthe user obtain information as to the location and other pertinentfeatures of the target and its important surroundings, (3) how does theuser lock onto that target so that the user has the assurance he isaffecting the intended target, (4) how does the user localize the effectto the target site, (5) how does the user treat a large number ofindividual targets, whether continuously connected, piecewise user treata large number of individual targets, whether continuously connected,piecewise connected, or disconnected, (6) how does the user assess theeffect of the intervention, (7) how does the user correct errorscommitted either during the course of the intervention or as a result ofprevious interventions, (8) how does the user react to changingconditions during the course of the intervention to ensure the desiredresult, and (9) how is safety ensured consistent with U.S. Food and DrugAgency regulations for medical instruments and good commercial practiceguidelines for industrial applications.

Of particular interest are medical interventions such as surgicalprocedures described by Sklar et al. (U.S. Pat. No. 5,098,426 and U.S.patent application Ser. No. 475,657 (now abandoned), which areincorporated herein by reference). Although many different kinds ofsurgery fall within the scope of the present invention, attention isdrawn to corneal refractive surgery in ophthalmology for the treatmentof myopia, hyperopia, and astigmatism.

For corneal refractive surgery, the above nine considerations reduce tothe following objectives (in accordance with the present inventiondescribed below): (1) identify the location on or in the cornea to betreated, (2) assure that the target is at the desired distance from theapparatus, determine the topography of the cornea, and determine thelocation of sensitive tissues to be avoided, (3) identify, quantify, andpursue the motion of suitable part of the cornea which can provide areference landmark that will not be altered as a result of the surgicalintervention and, likewise, the depth of variations (for example,distance form the corneal surface to the front objective lens changingdue to blood pressure pulses) of the corneal surface with respect to theapparatus such that said motions become transparent to the user of theapparatus, (4) provide a laser beam which can be focused onto theprecise locations designated by the user such that peripheral damage islimited to within the tolerable levels both surrounding the target siteand along the laser beam path anterior and posterior to the target site,(5) provide a user interface wherein the user can either draw, adjust,or designate particular template patterns overlaid on a live video imageof the cornea and provide the means for converting the template patterninto a sequence of automatic motion instructions which will traverse thelaser beam to focus sequentially on a number of points in threedimensional space which will in turn replicate the designated templatepattern into the corresponding surgical intervention, (6) assure thatitems (1)-(3) above can be performed continuously during the course ofand subsequent to the surgery to monitor the evolution of the pertinentcorneal surface and provide a means of accurate comparison betweenpre-operative and post-operative conditions, (7) ensure that thestructural and physiological damage caused by the surgery to the patientis sufficiently small to permit continued interventions on the same eye,(8) automate the interaction between the various components so thattheir use is transparent to the user and so that sufficiently fastelectronics accelerate completion of the surgical intervention withinpre-selected error tolerances, and (9) provide dependable, fail-safesafety features of sufficiently short reaction times to prevent anychance of injury to sensitive corneal tissues. With these objectivesfulfilled, the speed of surgery will no longer be limited by humanperception delay and response times but by the capability of theapparatus to recognize changing patterns and adjust to the newconditions. Equally important, the accuracy of the surgery will not beconstrained by the bounds of human dexterity, but by the mechanicalresolution, precision, and response of advanced electro-optical andelectromechanical systems.

There are substantial number of different functions which the apparatusof the present invention addresses. Each of the complementary and attimes competing, functions requires its own technologies andcorresponding subassemblies. The present invention describes how thesevarious technologies integrate into a unified workstation to performspecific interventions most efficaciously. For example, for cornealrefractive surgery, as per (1) and (2) above, identify the location tobe treated on or in the cornea, the surgeon/user would use a combinationof video imaging and automated diagnostic devices as described in Sklaret al. (U.S. Pat. No. 5,098,426 and U.S. patent application Ser. No.475,657 (now abandoned)), depth ranging techniques as described inFountain (U.S. Pat. No. 5,162,641), surface topographical techniques, asdescribed in Sklar (U.S. Pat. No. 5,054,907) together with signalenhancement techniques for obtaining curvatures and charting thecontours of the corneal surface as described by McMillan and Sklar (U.S.Pat. No. 5,170,193), profilometry methods as disclosed by McMillan etal. (U.S. Pat. No. 5,283,598), image stabilization techniques asdescribed by Fountain (U.S. Pat. No. 5,162,641), which may all becombined using techniques as described by Sklar et al. (U.S. Pat. No.5,098,426 and U.S. patent application Ser. No. 475,657 (now abandoned)).All of the above listed patent applications and the patent of Fountain(U.S. Pat. No. 5,391,165) are herein incorporated by reference.

Aspects of the above-referenced disclosures are further used to providemeans of satisfying the key aspects (3)-(9) noted above, such asverification of target distance from the apparatus, tracking the motionof the cornea in three dimensions, providing a laser whose parameterscan be tuned to selectively generate photodisruption of tissues orphotocoagulation as desired, automatically targeting and aiming thelaser beam to precise locations, and supplying a surgeon/user with arelatively simple means of using the apparatus through a computerinterface.

It is well known that visible light, which is passed without significantattenuation through most ophthalmic tissues, can be made to cause aplasma breakdown anywhere within eye tissue whenever the laser pulse canbe focused to sufficiently high irradiance and fluence levels to supportan avalanche process. The ensuing localized photodisruption isaccomplished by using a strongly focused laser beam such that only inthe immediate focal zone is the electric field sufficiently strong tocause ionization and nowhere else. By using short pulses of controllablysmall laser energy, the damage region can be limited in a predictablemanner while still guaranteeing the peak power necessary for localizedionization.

Furthermore, was lasers of increasingly higher repetition rate becomingavailable, the sometimes intricate patterns desired for a given surgicalprocedure can be accomplished much faster than the capabilities of asurgeon manually to aim and fire recursively. In prior systems andprocedures, the surgeon would aim at a target, verify his alignment, andif the target had not moved, then fire the laser. He would then move onto the next target, and repeat the process. Thus, the limiting factor tothe duration of the operation under these prior procedures was thesurgeon's reaction time while he focused on a target and the patient'smovement while the surgeon found his target and reacted to the targetrecognition by firing the laser. In practice, a surgeon/user canmanually observe, identify, move the laser focus to aim, and fire alaser at not more than two shots per second.

By contrast, a key object of the instrument and system of the presentinvention is to stabilize the motion of the patient by use of anautomated target acquisition and tracking system which allows thesurgeon to predetermine his firing pattern based on an image which isautomatically stabilized over time. The only limitations in time withthe system of the present invention relate to the repetition rate of thelaser itself, and the ability of the tracking system to successfullystabilize the image to within the requisite error tolerances for safetyand efficacy, while providing a means to automatically interrupt laserfiring if the target is not found when a pulse is to be fired. Thus,where it would take several hours for a surgeon/user to execute a givennumber of shots manually (ignoring fatigue factors), only a few minuteswould be required to perform the same procedure when automaticverification of focal point position and target tracking are providedwithin the device.

It is an object of the present invention to accommodate the mostdemanding tolerances in laser surgery, particularly eye surgery but alsofor other medical specialties, through a method, apparatus and systemfor high-precision laser surgery which provides the surgeon “live” videoimages containing supporting diagnostic information about depth andposition at which a surgical laser will be fired. In a computer, thefull information content of a given signal is interpreted so as toprovide this supporting diagnostic information, and the resultingaccuracy achievable is within a few human cells or better.

The system, apparatus and method of the present invention for precisionlaser surgery, particularly ophthalmic surgery, take a fully integratedapproach based on a number of different instrumental functions combinedwithin a single, fully automated unit. For example, previousconventional diagnostic instruments available to the ophthalmic surgeonhave included several different apparatus designed to provide thesurgeon/user limited measurement information regarding the cornea of theeye, such as the corneoscope, the keratometer, and the pachometer. Thecorneoscope provides contour levels on the outer surface of the cornea,or corneal epithelial surface, derived, typically, from projectedconcentric illumination rings. The keratometer gives cross sectionalcurvatures of the epithelial surface lens of the eye—the cornealepithelium surface. Only one group of points is examined, giving verylimited information. Pachometers are used to measure the central axisthicknesses of the cornea and anterior chamber.

The diagnostic functions fulfilled by these devices are instrumental tocharacterizing the subject tissue in sufficient detail to allow thesurgeon/user to perform high precision ophthalmic surgery.Unfortunately, these and other similar instruments require considerabletime to operate. Further, their use required near-total immobilizationof the eye or, alternatively, the surgeon/user had to be satisfied withinherent inaccuracies; the immobilization methods thus determined thelimitations on the accuracy and efficacy of eye surgery. Nor did thedifferent apparatus lend themselves to being combined into one smoothlyoperating instrument. For all of the above reasons, operation at timescales matched to the actual motions of the tissues targeted for therapyand/or limited by the fastest human response times to those motions(“real time”) has not been possible with any of the conventionalinstruments used to date.

By contrast, the methods and apparatus disclosed herein, aim toincorporate a mapping and topography means for reconstructing thecorneal surface shape and thickness across the entire cornea. It isfurthermore within the scope of the present invention to provide suchglobal measurements of the corneal refractive power without sacrificinglocal accuracies and while maintaining sufficient working distancebetween the eye and the front optical element of the instrument(objective lens), said measurements to be executed on-line within timescales not limited to human response times. Most standard profilometrytechniques were judged inadequate per the above requirements, requiringcompromises in either accuracies of the computed curvatures (such as,e.g., standard ‘k’ readings of keratometers), speed and ease ofoperation (scanning confocal microscopes) or left no working distancefor the ophthalmologist (corneoscopes and keratoscopes based on “placidodisk” illumination patterns). It is therefore a key objective of thepresent invention to include a new topography assembly that can overcomethe limitations of existing instruments while combining, on-line, and ina cost effective manner, many of the functions of conventionaldiagnostic instruments presently available to the surgeon, as anintegral part of a complete surgical laser unit.

In one embodiment of the present invention, the corneal refractive poweris measured using a unique projection and profilometry technique coupledwith signal enhancement methods for surface reconstruction as disclosedby McMillan and Sklar in U.S. Pat. No. 5,170,193 and further extended inlarger corneal cross-sections via techniques described in McMillan etal. in U.S. Pat. No. 5,283,598, both incorporated herein by reference.In another embodiment, digitized slit lamp video images are used tomeasure the local radii of curvature across the entire corneal surfaceas well as the thickness of the cornea, with no built-in a-prioriassumptions about the corneal shape. Both embodiments of the topographysystem benefit greatly from the availability of 3-D tracking capabilitycontained within the apparatus. The feature allows elimination of manyof the errors and ambiguities that tend to compromise the accuracy ofeven the best currently available instruments utilizing fine point edgeextraction and advanced surface fitting techniques. With thecomputerized topographic methods of the present invention, surfaces canbe reconstructed (and viewed in 3-D) with accuracies that go well beyondthe approximate photokeratometric and pathometry readings as advocatedby L'Esperance (U.S. Pat. No. 4,669,466), or even the more sophisticated(but complex) corneal mapping methods as disclosed by Bille (U.S. Pat.No. 5,062,702) and Baron (U.S. Pat. No. 4,761,071).

While tissue topography is a necessary diagnostic tool for measuringparameters instrumental to defining templates for the surgery (e.g.,refractive power), such instrumentation is not conducive to use duringsurgery, but rather before and after surgery. Also, the information thusobtained is limited to those parameters characteristic of surfacetopography (such as radii of curvature of the anterior and/or posteriorlayers of the cornea or lens). Yet, in many cases, it is desirable tosimultaneously image the target area and deposit laser energy at aspecific location within the tissue itself. To allow reliable, on-linemonitoring of a given surgical procedure, additional mapping and imagingmeans must therefore be incorporated. The imaging means is intended torecord, in three-dimensions, the location of significant features of thetissue to be operated upon, including features located well within thesubject tissue. It is therefore another object of the present inventionto provide continuously updated video images to be presented to thesurgeon/user as the surgery progresses, said images to be produced in acost effective manner yet compatible with high resolution and highmagnification across a large field of view and at sufficiently lowillumination levels to prevent any discomfort to the patient.

The imaging system, or the surgical microscope, requires viewing thereflected light form the cornea, which has two components: (a) specular(or mirror) reflection from a smooth surface, which returns the light atan angle opposite the angle of incidence about the normal from thesurface and also preserves the polarization of the incident beam, and(b) diffuse reflection, in which light returned from a rough surface orinhomogeneous material is scattered in all directions and loses thepolarization of the incident beam. No surface or material is perfectlysmooth or rough; thus all reflected light has a specular and a scatteredcomponent. In the case of the cornea there is a strong specularreflection from the front surface/tear layer and weak scattered lightfrom the cellular membranes below. Various standard ‘specularmicroscopes’ have been used to suppress the front surface reflection. Wehave chosen a combination of techniques: some aim at observing thecombined reflections without differentiating between specular or diffusesignals (for operations at or in immediate proximity to the surface ofthe cornea); in others the surface is illuminated with polarized light,with the reflected images then microscopically viewed through a crossedpolarizer for operation within deeper layers, after selectivelyfiltering the more anterior reflections. A rejection of the polarizedcomponent can thus be achieved, greatly enhancing resolution at lowenough light levels to prevent any discomfort to the patient. In eitherembodiment, the imaging system contained within the apparatus of theinvention represents a significant improvement over standard “slit lamp”microscopes such as are in use with most ophthalmic laser systems.

Other efforts at imaging the eye, such as performed with HeidelbergInstrument Confocal Microscope, or as described by Bille (U.S. Pat. No.4,579,430), either do not lend themselves to inclusion as part of anon-line, cost effective, integrated surgical system (for the former), orrely upon scanning techniques which do not capture an image of the eyeat a given instant in time (for the latter). The method of the presentinvention benefits from having an instantaneous full image rather than ascanned image; for full efficacy, the method does, however, require thatthe targeted area be stabilized with respect to both the imaging and thelaser focal region, so as to enhance the accuracy of laser deposition intandem with the viewing sharpness.

Tracking is therefore considered a critical element of a system designedonto only to diagnose, but also select treatment, position the treatmentbeam and image the tissue simultaneously with the treatment, whileassuring safety at all times. In the case of corneal surgery, movementsof the eye must be followed by a tracking system and, suing dedicatedmicroprocessors, at closed-loop refresh speeds surpassing thoseachievable by unaided human inspection, by at least an order ofmagnitude. Tracking by following the subject eye tissue, i.e.,recognizing new locations of the same tissue and readjusting the imagingsystem and the surgical laser aim to the new location, assures that thelaser, when firing through a prescribed pattern, will not deviate fromthe pattern an unacceptable distance. In preferred embodiments of theinvention, this distance is held within 5 μm in all situations duringophthalmic surgery, which sets a margin of error for the procedure. Itis possible that with future use and experimentation, it may be foundthat either more stringent or alternatively more lax displacement errortolerances are desirable to improve overall system performance.

Stabilization of a moving target requires defining the target,characterizing the motion of the target, and readjusting the aim of theapparatus of the present invention repeatedly in a closed-loop system.To meet accuracy goals also requires that the moving parts within theapparatus not contribute internal vibrations, overshoots, or othersources of positioning error which could cumulate to an error in excessof the prescribed dispositioning tolerances. There have been severalprevious attempts at achieving this result. Crane and Steel (AppliedOptics, 24, pp. 527, 1985) and Crane (U.S. Pat. No. 4,443,075) describeda dual Purkinje projection technique to compare the displacement of twodifferent-order Purkinje projections over time, and a repositioningapparatus to adjust the isometric transformation corresponding to themotion. The tracking methods disclosed therein are based on a fundusillumination and monitoring device that aspires to distinguishtranslational from rotational eye movements, thus stabilizing anilluminating spot on the retina. However, localization of the Purkinjepoints can be influenced by transient relative motions between thevarious optical elements of the eye and may provide significantlyfictitious position information for identifying the surface of thecornea. Motility studies as described by Katz et al. (American Journalof Ophthamology, 107: 356-360, “Slow Saccades in the AcquiredImmunodeficiency Syndrome”, April 1989) analyze the translations of animage on the retina from which the resulting coordinate transformationcan be computed and galvanometric driven mirrors can be repositioned. Inaddition to the fictitious information discussed above due to relativemotions between different layers of the eye, the galvanometer drivesdescribed by Katz usually are associated with considerable overshootproblems. Since saccades can be described as highly accelerated motionswith constantly changing directions, overshoot errors can easily lead tounacceptable errors.

Bille et al. (U.S. Pat. No. 4,848,340) describes a method of following amark on the epithelial surface of the cornea, supposedly in proximity ofthe targeted surface material. However, in one of the uses of thepresent invention, a mark made on the epithelial surface would changeits absolute location due to changes in the structure and shape of thematerial, caused by use of the instrument itself rather than by eyemotions. Therefore, a target tracking and laser positioning mechanismthat relies on a mark on the surface of the cornea in order to performcorneal surgery such as described by Bille's tracking method would beexpected to lead to misdirected positioning of laser lesions below thesurface when combined with any suitable focused laser, as intended inone of the uses of the present invention. Moreover, one of the featuresof the present invention is to be able to perform surgery inside thecornea without having to incise the cornea. The main advantages of sucha procedure are in avoiding exposure of the eye to infection and inminimizing patient discomfort. It would hence be counterproductive tomark the surface of the cornea for the purpose of following the motionof said mark. In another embodiment taught by Bille et al., the trackingis based on a reference provided by either on the eye's symmetry axis,or the eye's visual axis, with an empirically determined offset betweenthe two. Tracking is then accomplished by monitoring the reflection formthe apex of the cornea, thus avoiding the need to mark the eye, and/orrely solely on patient fixation. However, with this technique, as in thepreferred embodiment taught by Bille et al., the tracking does notfollow tissue features generally at the same location as the targetedsurgical site on or inside the eye. Instead, Bille et al.'s techniquestrack reference points that are, in all cases, separate, remote from andmay be unrelated to the targeted surgical site. Such methods compromiseaccuracy of tracking in direct proportion to the degree of theirremoteness relative to the surgical site. Therefore, they do notadequately provide for the fact that the eye is a living tissue, movingand changing shape to some extent constantly. Tracking a single point onthe cornea, when the cornea itself actually shifts considerably on theeye, thus cannot be expected to reflect positional change of thetargeted surgical site.

By contrast, in the preferred embodiment of the present invention thetracking information is obtained through means contiguous to the targetregion, which is mechanically and structurally considered as part of thecornea, but is unlikely to be affected by the course of the surgery andcan thus provide a significant representation of non-surgically induceddisplacements. This is a critical feature of the tracking methoddisclosed herein, in that involuntary motions of the eye (such as arecaused by blood vessel pulsing) can now be accurately accommodated,unlike techniques that rely on remote reference points.

The accuracy of the apparatus and system of the invention preferably iswithin 5 μm, as determined by a closed-loop system which incorporatesactual measurement of the target position within the loop. (For example,a microstepper motor based assembly may have a single step resolution of0.1 μm verified against a motor encoder, but thermal gradients in theslides may yield greater variations. Moreover, position of the slide canbe verified via an independent optical encoder, but the randomvibrations of the target can invalidate the relative accuracy of themotor.) Thus, the surgeon has knowledge of the shape of tissues withinthe field of view and the precise location of where he is aiming theinstrument within those structures, to an accuracy of 5 μm. Suchprecision was not attainable in a systematic, predictable manner withany of the prior instruments or practices used. The present inventionthus seeks to obviate the need for binocular vision used to obtainstereoptic images in some prior methods (see., e.g., Crane, U.S. Pat.No. 4,443,075).

In a preferred embodiment of the invention, the instrument also ensuresthat a laser pulse is fired only upon command of the computerizedcontroller and after the system has verified that the tracking assemblyis still locked onto the desired location, that the energy being emittedby the laser falls within prescribed error tolerances, and that theaiming and focusing mechanisms have reach their requested settings.There is no need to separate aiming beam. In one embodiment of thepresent system, the method of parallax ranging is implemented to map outsurfaces posterior to the cornea, but preceding actual treatment.

Safety is a very important consideration with laser surgery. In priorsurgical systems and procedures, some safety shut-off procedures forlaser firing have depended upon human reaction time, such as the use ofa surgeon's foot pedal for disabling the instrument when a situationarises which would make firing unsafe. In ophthalmology, someinstruments have relied as a safety feature on a pressure sensor locatedwhere the patient's forehead normally rests during surgery. Ifinsufficient pressure were detected by the sensor, the instrument wouldbe disabled from firing.

Such prior safety systems have inherently had slow reaction times, andhave not been able to react quickly enough to all of the variousproblems which can arise during a firing sequence. This is a criticalconcern in ophthalmic surgery, especially where specific surgicalprocedures are to be performed near sensitive non-regenerative tissues,such as the corneal endothelium layer and the optic nerve. In contrast,the target capture and tracking system of the present invention makesavailable a new and highly dependable safety system. If for any reason,either prior to or during a given surgical procedure, the trackingsystem loses its target, the laser is disabled from firing. Variousoptions are available for blocking emission from the apparatus once thetracking assembly has verified the loss of a tracking signal.

No previous surgical laser system has employed the efficaciouscombination of features as disclosed herein. For example, in previousart, Bille et al. (U.S. Pat. No. 4,848,340) and Crane (U.S. Pat. No.4,443,075) taught tracking techniques to follow tissue movements whichmight occur during surgery, but did not teach simultaneous 3D imagingwithin the tissue to monitor the effects of surgery on the tissue andprovide requisite safety margins; L'Esperance (U.S. Pat. Nos. 4,669,466and 4,665,913) also did not suggest any aspects of 3D imaging, teachingonly laser surgery on the anterior surface of the cornea; Bille (U.S.Pat. No. 4,579,430) shows a retina scanner, but does not teachsimultaneous tracking. Bille et al. (U.S. Pat. No. 4,881,808) teach animaging system and incorporate a tracker and a beam guidance system byreference (per U.S. Pat. Nos. 4,848,340 and 4,901,718, respectively) butfail to address the very difficult challenges involved in achieving asmooth combination of all these aspects into a single surgical laserunit with built-in high reliability features. By contrast, it is theunique integration of several such diverse aspects (including mapping,imaging, tracking, precision laser cutting and user interface),precisely yet inexpensively, into a fully automated workstation, theuses of which are transparent to the user, that is the main subject ofthe present invention. The methods and apparatus disclosed herein arethus expected to enhance the capabilities of a surgeon/user inaccomplishing increasingly more precise surgical interventions in afaster and more predictable manner. Enhanced safety is expected to be anatural outcome of the methods and apparatus taught herein in that thesurgery will be performed without many of the risks associated withcompeting methods and apparatus as described by L'Esperance (U.S. Pat.Nos. 4,669,466 and 4,665,913), Srinivasian (U.S. Pat. No. 4,784,135),Bille et al. (U.S. Pat. Nos. 4,848,340; 4,881,808; and 4,907,586),Frankhauser (U.S. Pat. No. 4,391,275), Aron-Rosa (U.S. Pat. No.4,309,998), Crane (U.S. Pat. No. 4,443,075), and others.

SUMMARY OF THE INVENTION

An embodiment of the present invention is herein disclosed, comprising amethod, apparatus, and system for precision laser based microsurgery orother laser-based micromachining, and including the following elements,each of which is described below.

A final objective (lens), the axial position of which relative to thetear layer of the corneal vertex (or to a more general target), is heldconstant by an axial tracking means, and through which pass all opticalradiations emitted or accepted by the system. (2) An axial trackingmeans (including associated optics) for maintaining constant separationbetween the final objective and its target (which is to be distinguishedfrom the (common) target for the treatment means and the parallaxranging means, and also from the target for the viewing means) as thattarget moves axially along the final objective's centerline. The axialtracking means includes a compensation means to preclude it from beingadversely affected by the transverse tracking means. (3) A transversetracking means (including optics) for maintaining constant aimingbetween the treatment and parallax ranging means and their (common)target, and between the viewing means and its target, as those targetsmove (together) transversely to the final objective's centerline. (4) Atreatment means for effecting the actual lasermicrosurgery/micromachining, including a laser, laser-beam directingoptics, a treatment aiming means (with optics), and a treatment focusingmeans (also including optics), all of which are actuated by acomputerized control means. (5) A parallax ranging means, which sharesoptics for the treatment aiming and focusing means, for positioning thecommon focus of the treatment parallax ranging means at a desiredlocation (independent of the target identified above) by use of theviewing means and without requiring the actual operation to beperformed. (6) A viewing means, comprising optics and a low-light-levelTV camera, for presenting to the surgeon/user, on the display means, anadjustably magnified image of the volume adjacent to the viewing target,which target may be chosen by the user independently of the othertargets identified above. (7) A computerized control means, including auser interface presented on the display means, which performscalculations and accepts and issues signals in order to execute thevarious functions of the overall system. (8) A display means forpresenting to the surgeon/user the image from the viewing means pluscomputer-generated overlays from the user interface: such overlaysinclude not only menus but also textual and graphic representations ofaspects such as the topography of the cornea (or more general surfacesassociated with the various targets) and the microsurgery/micromachiningtemplates to be used. (9) A profiling means, including optics, one ormore (patterned) profilometry illuminators, and a TV camera, to generatethe data from which the computerized control means can calculate thetopography of the cornea (or, in other embodiments, a more generalsurface). (10) An output measurement means to measure parameters of thelaser radiation delivered to the eye of the patient or the workpiece.(11) Various illumination means, such as the profilometry illuminators,the coaxial illuminator, and the slit illuminator, to provide the lightsource(s) for the profilometry means, the transverse tracking means andthe viewing means.

The present invention is expected to be useful in a variety of medicalspecialties, especially wherever the positioning accuracy of laserlesions is critical and where accurate containment of the spatial extentof a laser lesion is desirable. Much of the following discussions willbe directed at ophthalmic applications and specifically cornealrefractive surgery. This should not be viewed as a limitation on theapplicability of the apparatus and method of the present invention.Alternate embodiments of the invention are expected to play a role inseveral other medical applications.

The system is also useful for non-medical operations, such as industrialoperations, especially micromachining and short repair of microchips,wherein a focused laser beam is used to perform high precisionoperations on an object subject to movement, or in the automatedinspection and correction of errors in the manufacture ofmicroprocessors and high-density integrated circuits.

In specific applications to corneal procedures, the present invention isintended to provide a means by which an ophthalmologist can (a) observethe patient's eye at both low magnification to orient the procedure andat progressively higher magnification to provide great resolution forfiner and more accurate procedures, (b) access on-line diagnosticinformation as to the shape of one or more relevant surfaces or oftissue layers to be treated, (c) describe a pattern of shots to effect aparticular lesion shape without requiring manual aiming of each shot bythe surgeon, (d) provide a therapeutic laser beam propagating through abeam steering and focusing delivery system which can localize the laserlesions at a particular depth in the immediate neighborhood of the laserfocal point without appreciable damage elsewhere and with minimalperipheral necrosis or thermal damage surrounding the affected volume,and (e) provide a target tracking system that can minimize the error inpositioning the pattern of the laser lesion in a moving target.

In the user interface, a video monitor screen is provided in front ofthe surgeon, and the screen provides a variety of choices for imagingand diagnostic information. Among the selections available to theophthalmologist, for example, is a live video image of the eyesuperimposed over sectional perspectives of the shape of the cornealanterior surface and displayed along with the location where theproposed surgical lesion is situated. Another choice is to display awire-mesh contour elevation map of said corneal surface together with animbedded display of the proposed lesion. These selections can all beenlarged by using the zoom option which augments the live video image,and proportionally also the wire-mesh surface contour, the perspectiveviews of the surface, and all other relevant diagnostics.

Additionally, a library of patterns is available so that the computercan generate templates based on the optical correction prescribed(generated off-line by the physician's “refraction” of the patient) andthe measured topography (which templates will automatically correct foredge effects, based on built-in expert-system computational capability).The surgeon/user can move the templates on the screen by means of atrackball, mouse, or other standard pointing device for manipulatingpoints on a video screen and thus, define the shape of the desiredlesion and situate it at the optimal treatment location. These templatesserve the additional function, once finally approved by thesurgeon/user, of automatically controlling the path of the firing of thelaser as well as the size and location of the laser-generated lesions tobe formed in the course of the microsurgery. Since particular templatescan be stored in computer memory, the surgeon/user may, as experiencewith the apparatus develops, draw on a bank of prior knowledge relatingto a particular form of microsurgery, such as ophthalmic surgerydirected to a specific type of correction. A physician may thereforechoose to select from a set of pre-existing templates containing hispreferred prescriptions, lay the template, in effect, on thecomputer-generated image of the region, and resize and/or re-scale thetemplate to match the particular patient/eye characteristics. Thesurgery can then be executed automatically in a precisely controlledmanner, based on the computer programming sense.

Such a pre-existing library of templates is also useful in the executionof controlled animal studies. It should be noted, however, that withoutthe accompanying three-dimensional targeting capability and theautomatic image stabilization means contained within the hardware of thepresent invention, the utility of template-generated surgery alone wouldbe severely limited either to no-sensitive tissues (where high threedimensional precision is not usually a consideration) or to relativelystationary or immobilized targets (not usually available at highmagnification in a biological system which is “alive).

In another embodiment of the methods and hardware of the presentinvention, templates can also be generated and stored in similar mannerfor procedures other than corneal refractive surgery, includingiridotomy, posterior capsulotomy, trabeculoplasty, keratotomy, and thelike.

Among the advantages of the present invention is the modular design ofthe multiple assemblies. The multiple assemblies are each individuallysupported on kinematic mounts. These mounts allow for the separateconstruction of the multiple assemblies, their alignment to tooling jigsindividually, and the precise “hard-aligning” of the multiple assembliesinto a complex optical system. Although such kinematic mounts can add,somewhat, to manufacturing costs, they save considerable alignment timeduring the assembly of the apparatus and provide a greater measure ofreliability that the apparatus shall remain in operational alignmentduring continued use by non-technical surgeon/users.

Using the instruments of the present invention, the surgeon can generatea proposed pattern of therapeutic treatment, can compare the pattern tothe actual tissues targeted, can compare his proposed surgery with whatother surgeons have done in similar situations, and can still have theassurance that when he is finally satisfied with the proposed procedure,he can push a button to cause the desired surgery to be carried out at ahigh rate of independently targeted shots per second. This speedminimizes the risk during surgery at catastrophic patient motion.

In addition, the surgeon has at his disposal a fast reliable safetymeans, whereby the laser firing is interrupted automatically, should anyconditions arise to warrant such interruption of the procedure. Thesurgeon can also temporarily disable the laser from firing at an pointduring the course of the surgery via suitable manual controls.

The tracking subsystem of the invention serves two important purposes:it tracks and follows the movements of the patient's tissue—not only thevoluntary movements which can be damped with specialize treatment, butalso the involuntary movements which are more difficult to control on aliving specimen—and continuously re-presents an image of the samesection of tissue. Thus, the surgeon/user is provided a continuous,substantially immobilized view of that tissue regardless of patientmovements; and it further provides a fail-safe means for immediatelystopping the action of the surgical laser beam in the even the trackingis lost, i.e., the tissue is not recognized by the tracking algorithmfollowing the motion, per the discussion on safety features above.

In accordance with the invention, fast imaging and tracking are achievedusing the combined effects of a pivoting tracking mirror which may beunder the directional control of a piezoelectric or electromagnetictransducer, or other rapid servo device to pursue eye motions in a planeperpendicular to the optical axis of the final focusing lens (alsoreferred to herein as the X-Y plane), coupled with a motor drive whichtranslates the otherwise fixed final focusing lens assembly along theaxial direction of the final focusing lens, herein denoted as the Zaxis. Thus, three dimensional motions which fall within the domain ofcapture of the tracking system can be observed, pursued and captured.

Fast response times are possible with the described embodiment of theinvention, limited by the ultimate speed of the tracking detector, thecomputational capabilities of the apparatus microprocessors and datatransfer rates, and the moment of inertia of the tracking servo mirror.It has been determined that such closed-loop target recognition andtracking should occur at least at a rate of approximately 20-to-40 Hz inorder to compensate for involuntary eye motion and thus, provide asignificant improvement over human reaction times. Tracking rates on theorder of 100 Hz for full amplitudes on the order of >1 mm (about 5°) inthe transverse direction and in excess of 40 Hz over a range of +2 mmaxially, would ultimately be achievable with some improvements based onthe methods and system of the present system.

In a preferred embodiment of the present invention, the trackingsensors, or detectors, in combination with their circuitry, should becapable of high spatial resolution. Examples are linear position sensingdetectors and quadrant detectors. For corneal refractive surgery, thelimbus of the eye provides a landmark ideally suited for such detectors.In the retina, landmarks such as the optic disk, or vesselconfigurations can similarly provide landmarks upon which a magnifiedview can serve as the tracking landmark. In the present invention, anynatural eye feature located in proximity of and structurally contiguousto the target site will serve as the tracking landmark. The importantobservation is that the location of the tracking landmark must respondto forces and pressures in a manner similar to the targeted tissues, yetit cannot be coincident with the precise target site itself, since thissite will change during the course of the surgery.

Since the limbus is the outer edge of the cornea, it is expected thatthe limbus will respond to changes in position in a similar manner toother corneal tissues. The limbus further has the advantage of beingcontiguous to the sclera. Correspondingly, it is expected that thetransient displacements occasioned by the impact of the laser pulse onthe target site will be damped sufficiently at the limbus so as to notinduce fictitious tracking signals. Such fictitious tracking signalswould normally be a frequent observation if the present invention wereto use, for example, a mark on the surface of the cornea in the vicinityof the operative site or a remote symmetry axis. Similar considerationsapply when selecting a tracking landmark in other eye segments.

By incorporating intensified cameras, the present instrument and systemis of high sensitivity, requiring only low levels of illumination, andproduces video images of high contrast and high resolution. Illuminationlevels are kept well within established safety levels for the human eye.With the optics of the present system the patient's tissue is observedfrom an appreciable distance, sufficient for comfort to the patient evenduring surgery, and sufficient to permit the surgeon/user ready accessto the patient in case of emergency, to insure safety at all times, toreassure the patient, or for any other reason which the surgeon/user mayfeel justifiable.

Zoom optics are included so that the physician an select a range ofmagnification for the video image, which maybe from about, say 15× to200×. Different zooming ranges may be appropriate for different types ofsurgical procedures while maintaining an overall zooming capability ofapproximately 15-fold. The viewing system may be refocused in depth aswell as transversely, independent of the treatment beam, as desired.

In one embodiment of the present invention, a system for use inophthalmic laser surgery includes a laser source with sufficient outputpower to effect a desired type of surgery in the ocular tissue, alongwith an optical path means for delivering the laser beam, including beamdirecting and focusing means for controlling the aim and depth of focusof the laser beam. In a preferred embodiment of the present invention, alaser firing up to 250 shots per second is employed. Such a laser devicecan generate an intricate pattern consisting of 50,000 shots aimedseparately at different locations in under 4 minutes. For most types ofophthalmic surgery procedures falling in the domain of application forthe system disclosed herein, the method of deposition of the laser pulseenergy onto the target site calls for achieving irradiances at thetarget site above the threshold for ionization of molecules within thetarget site and giving rise to an avalanche process culminating inplasma formation. Since the maximal diameter of the lesion willconsequently not be determined by the theoretical spot size of the laserbeam but by the maximal outward expansion of the cavitation inducedduring plasma collapse, and since the maximal lesion capacity of theplasma is related to the amount of energy transferred into the plasmavolume (and subsequently into a shock wave) by the laser pulse,considerable attention is needed to maintain the laser pulse energywithin narrow variation tolerances. In one preferred embodiment of thepresent invention, this is achieved by a closed feedback loop, whereineach laser pulse emitted by the system is sampled to determine theactual energy being emitted. Any trends in emission energy can thus beidentified allowing subsequent emitted pulse energies to be adjustedaccordingly.

U.S. Food and Drug Agency regulations for medical laser devicescurrently require manufacturers of said devices to provide a means formeasuring the output delivered to the human body to within an accuracyof +/−20%. There is no specification on emission tolerances for thelaser beyond the constraints of safety and efficacy. However,verification of average pulse emission does not preclude 50% variationsbetween consecutive pulses in a firing sequence. Such variation range isone of the reasons why “misfires” occur in many ophthalmic devices. Itis not that the laser failed to fire, but that insufficient energy wasemitted to achieve the desired or expected result because of unforeseenand undetected energy variations. For an automated system, such as thepresent invention, the emission for the laser needs to be monitored andadjusted to achieve far narrower pulse-to-pulse error tolerances.

In summary, it is among the objects of the present invention to greatlyimprove the accuracy, speed, range, reliability, versatility, safety,and efficacy of laser surgery, particularly ophthalmic surgery, by asystem and instrument which continuously presents information to thesurgeon/user during surgery as to the precise location, aim, and depthof the surgical laser and also as to surrounding features of the subjecttissue, in three-dimensions. It is also an object of the invention totrack movements of the subject tissue during surgery, particularlycritical in eye surgery where eye movements can be very rapid andinvoluntary. It is further an object of the invention to provide a safemeans of first establishing a reproducible firing sequence positioned ina three-dimensional space, and then firing the sequence in highrepetition rates, thus obviating the time-consuming need to repetitivelyinspect, aim, and fire each shot before proceeding to the next target.Still another object is to provide a system applicable to non-medicalfields wherein a laser beam is used to effect a precise operation on atarget or series of targets subject to movement during the procedure.These and other objects, advantages, and features of the invention willbe apparent from the following description of preferred embodiments,considered along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an instrument or workstation for performingprecision laser surgery in accordance with the principles of the presentinvention. In FIG. 1 the workstation is configured for ophthalmicsurgery.

FIG. 2 is a block diagram of an instrument or workstation indicating thepath of the laser energy pulse as it propagates through the system alongwith the functions of control and information flow among various opticalcomponents, detectors, and controllers for monitoring the energy of thelaser pulse and maintaining the emission within prescribed narrow errortolerances.

FIG. 3 is a block diagram of the path for light traveling from and backto the depth ranging or Z-plane tracking means, together with the loopfor information flow to the computer control means and back to theposition means.

FIG. 4 is a block diagram showing the light path from the parallaxranging assembly to the eye and the control path from the imaging videocamera to the video monitoring display means. The light path from theeye back to the imaging camera is also indicated in this Fig.

FIG. 5 is a block diagram of the workstation in which the light pathsand control loops for the X-Y place tracking means are shown.

FIG. 5A shows the image of the iris incident on the two quadrantdetectors used in a preferred embodiment of the sensor for X-Y tracking.

FIG. 6 is a block diagram indicating the interplay of the imaging meanswith the video monitor display.

FIG. 7 is another block diagram indicating the light path between thetopography assembly and the eye together with the control loop andinterface with the video monitor display. The displays generated by thetopography loop depicted in this Fig. are overlayed the live image shownin FIG. 7 by the computer control assembly.

FIG. 8 is a scale drawing of one embodiment of the instrument of thepresent invention.

FIGS. 9 a-9 e represent three perspectives of an artistic rendition ofan ergonomic configuration of the workstation. The system was designedto accommodate the engineering subassemblies in a maximally compactmanner while providing a large amount of clear space for the patient.

FIG. 10 is a detailed block diagram illustrating the functionalinterdependence among the various optical subsystems.

FIG. 11 is a block diagram showing the sequence of control andinformation flow from the user interface elements to the firing of thelaser.

FIG. 12 is a photograph of a user interface screen showing a selectionof computer-generated patterns which can further be modified using“CAD/CAM-like” editing functions, such as are contained in a “utilities”module.

FIG. 13 is an illustration of a user interface screen showing a windowof a sample “treatment” menu used to select treatment eye segments, setlesion shapes, choose operating parameters corresponding to the templatedesignated procedure or other functions.

FIG. 14 is a photograph showing the same sample templates as FIG. 12,and highlighting an example of a pull-down “set parameters” menu.

FIG. 15 is a topographical representation of a three-dimensional eyesurface as seen from the user/interface screen, highlighting a sample“diagnostic” module.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

In the drawings, FIG. 1 shows a block diagram for the fundamentalassemblies of a complete precision laser surgery and/ordiagnostic/analytical instrument 10 in accordance with the principles ofthe present invention, in the form of a workstation. Not shown are thesupport station housing the video monitor means, the power supplies, thefire control/safety switch, and other accessories for the workstation.

Although the system, apparatus, and method of the invention areillustrated and discussed with reference to ophthalmic surgery anddiagnosis, it should be understood that the invention encompasses othertypes of medical diagnostic and surgical procedures, as well asnon-medical operations (e.g., semiconductor processing, such asprecision wafer fabrication, short repair using lasers and othermicromachining techniques.)

The instrument and system 10 of the invention include controls 16 for avision system and laser firing, enabling the surgeon/user to survey thetopography and internal features of the tissue to be operated upon (theeye in the illustrated workstation) via a video means 19, and, via thecomputerized control means, to precisely control the timing as well asthe direction, depth and spatial pattern of firing of a laser beam inthree-dimensions. As will be explained below, the surgeon may controlthe firing of the laser with “templates” which can be superimposed overan image of the tissue being operated upon, and which enable anautomatic tracing of desired laser firing pattern based upon priorexperience or a surgeon's insights with similar surgical procedures. Thetemplates may be pre-programmed or generated anew for each patient, asthe case requires.

The system also includes a final objective lens or focusing lens orfront lens 17 (an element of the microscope assembly, as explainedbelow), through which images are taken and through which the laser beamis directed at the subject tissue. In a preferred embodiment of thesystem, an axial illuminating light beam may be projected at the tissuethrough the topography assembly 98 and the final objective lens 17. Inother embodiments of the present invention, an off-axis slitilluminator, providing a ribbon-shaped illuminating light beam, may beused to augment and/or replace the axial illumination technique, (SeeHowland et al. “Noninvasive Assessment of the Visual System TopicalMeeting,” Santa Fe, Feb. 4-7, 1991) depending on the particular kind ofsurgical procedure or error tolerances required thereof. Th instrument10 may contain, in addition, the therapeutic laser 87, the surgicalmicroscope 86, an X-Y tracking assembly 85, a depth ranging microscope84, a parallax depth ranging assembly 82, various illuminators, and thebeam steering and focusing assembly 81. All of these assemblies share anoptical path defined by the final tracking mirror 72 and the lens 17.

Tracking mirror 72 represents a key element in the system, in that it isin the path of light (whether transmitted or reflected), generatedand/or acquired by all the various subassemblies of the workstation,excepting only the slit illuminator (of the alternate embodiment, notshown in FIG. 1). In alternate embodiments of the invention, thetracking mirror may be driven either piezoelectrically orelectromagnetically. A piezoelectric driver uses the change in shape ofa quartz crystal in response to an electric current to move the mirror.An electromagnetic driver uses a coil of wire in a magnetic field whichis made to move by passing an electric current through the coil. Theelectromagnetic driver is similar in function to a voice coil of anaudio speaker. In either embodiment, the speed (or, more accurately, theacceleration) of the entire tracking system is limited by the responseof the drivers and the mirror's moment of inertia.

Most of the major components and subassemblies, shown in the blockdiagram of FIG. 1, are disclosed separately and have been incorporatedherein by reference. However, the combination of these separateinventions into system 10, the methods by which they can be made to workin concert as an integrated unit, and the enhanced capabilities thisentails in a surgical environment are the subject of the presentinvention.

For example, the topography technique requires establishing preciselythe distance from the surface to be measured to the appropriateprincipal lane of the front focusing lens. Whereas there are severalmethods for establishing said distance, the modified confocal techniquedescribed by Fountain (U.S. Pat. No. 5,283,598) represents a preferredembodiment of such a measuring technique, incorporated by reference intothe present invention. Since in surgery the targets are live tissue andare continuously in motion, to achieve high levels of accuracy requiresthat the surface to be measured by way of the topography assembly alsoremain stable with respect to the measuring sensors located withintopography assembly 98, zoom video assembly 86, and the known focalpoint of laser 87. This is achieved by continuously adjusting theposition of final focusing lens 17 along the axial direction as furtherdescribed by Fountain in the '598 patent.

FIG. 2 shows the light path 71 as it emerges from laser 87, passesthrough the external energy regulator 83, is expanded and directed inthe beam steering and focusing assembly 81 as further described byFountain et al. in U.S. Pat. No. 5,391,165 and is aimed via trackingmirror 72 and through front focusing lens 17 onto the prescribed targetsite. In a preferred embodiment of the invention, tracking mirror 72will have an optical coating which will permit a small portion of thelaser energy to continue through tracking mirror 72, along path 73 to bedetected in energy monitoring assembly 80, as depicted in FIG. 2.

The pulse energy sensed in energy monitoring assembly 80 iselectronically relayed to the computer control assembly 16 which in turnanalyzes the output energy from laser 87 and adjusts the proportion oflaser energy of subsequent laser pulses to pass through energy regulator83. In an embodiment of the present invention, energy regulator 83 is apolarizer adjusted to be “crossed” with the polarized laser pulse,preceded by a rotatable half-wave retardation plate. Energy monitor 80consists of an integrating sphere and detector which can record energyon a pulse-by-pulse basis. The energy detector calculates weightedexponential moving averages, modified with a weighting factor, as wellas the rate of change of the running average. The accuracy ofmeasurement of the pulse energy is within 5%, based on calibrationagainst standard energy meters (e.g., Molectron, Scientech).

In a preferred embodiment of system 10, the steering, focusing, andaiming subassembly 81 may consist of a beam expander 22 that providesdepth of focus variations through change of collimation, and a dual setof Risley prisms (also known as Herschel prisms) 21 to steer and aim thebeam, as described in detail in the '165 patent by Fountain et al.(previously made of record).

Beam expander 22 may comprise a set of lenses 23, a stepper motor 41,and a slide 43 with 75 mm traverse corresponding to ˜25 mm in the eye.Beam focus accuracy to within 10 μm can be provided in this manner,based on standard optical components. The Risley prisms are selected aspreferred means of beam steering and directing because of lower momentof inertia and shorter lever arm as compared to alternatives, such asgimbaled mirrors. The lower moment of inertia inherently allows fasteraiming (which is enhanced by the use of cylindrical coordinates, thesebeing more natural for the eye than Cartesian coordinates), while theshorter lever arm permits aiming further off-axis without beam-clipping(vignetting) at the aperture of objective lens 17.

In a preferred embodiment of the invention, surgical laser 17 emitsradiation in the visible wavelength range to take advantage of thetransmission properties of visible light in the optically clear tissuesof the human eye. One preferred embodiment of the invention uses afrequency doubled Nd:YAG laser, producing sufficiently short durationpulses (shorter than a few hundred nanoseconds, and preferably shorterthan 10 nanoseconds) to limit the amount of energy required to ionizematerial as discussed further below.

In alternative embodiments, laser 87 may be one of several types offlashlamp- or diode-pumped solid-state lasers (such as, Nd:YAG, Nd:YLF,HoYLF, Er:YAG, alexandrite, Ti:sapphire or others) operating in thefundamental or a frequency-multiplied mode, a semiconductor laser, or anargon, excimer, nitrogen, dye, or any of a host of different laser, orcombinations thereof, currently available or in development. The presentinvention can be used with any of a wide variety of lasers by specifyingdifferent coatings where necessary for the optical surfaces. A quartzand magnesium fluoride focusing element is available as the element 17to accommodate ultraviolet lasers whether they be excimer lasers orfrequency shifted solid-state lasers. One of the features of the presentinvention is that is it is not laser specific, but represents a surgicalinstrument intended to enhance the efficacy of any therapeutic laser.Laser 87 preferably produces a pulsed beam which is controllable as tothe level of energy per pulse, pulse peak power, and repetition rate.For ophthalmic applications which do not seek to generate laser lesionsbelow the front surface of the cornea, or wherever incising the eye isan acceptable option as a preliminary or as part of the procedure, thenexcimer lasers, holmium lasers, carbon dioxide lasers, or some otherultraviolet or infrared laser may be an acceptable modality. In oneembodiment of the present invention, the surgeon is not restricted tosurface effects or to incising the eye. With the same visible wavelengthlaser (for example, a frequency doubled Nd:YAG) the surgeon can selectany tissue depth (whether on the corneal surface or below, whether onthe posterior lens capsule or in the lens nucleus) at which to generatean effect without the necessity of exchanging laser modalities fordifferent eye segments, provided there remains an optically clear pathto the targeted layer in the corresponding visible range.

In the event of a non-visible-wavelength laser beam is used (e.g.,strictly for ablating the front surface of the cornea, or strictly forcoagulating blood vessels in the retina, or strictly for photodisruptingmembranes on the posterior capsule) some variations in the opticalconfiguration of system 10 will likely be required.

FIG. 3 shows the information path for depth ranger assembly 84 thatmeasures the distance from front focusing lens 17 to the surface of theeye 69 and continuously adjusts the position of front focusing lens 17along path 88. In a preferred embodiment of the present invention, thepath length 88 over which front focusing lens 17 is adjusted is 5 mm.The system comprising subassembly 84 together with lens 17 and theintervening optics, is sometimes referred to herein as the confocalmicroscope. It uses optical elements in common with other equipment ofsystem 10, namely the tracking servo mirror 72 and beam splitters 65,66. Focusing lens 17 is adjusted as to focus, along a Z-axis, inresponse to shifts in the depth of the subject tissue feature, so thatthe system always returns to a focus on the corneal vertex 56 (the partof the cornea that is closest to the objective lens).

Included in the depth ranger assembly 84 are depth tracking or “Z-axis”tracking sensors 50 which detect a change in location of the surface 69as described by Fountain (in a U.S. Pat. No. 5,283,598, previouslyincorporated) and relay the information to the computer control assembly16 which computes a new desired position for front objective lensassembly 17 and issues instruction to a motor drive to relocate saidlens assembly 17 to the desired new location. A closed-loop is thusdescribed which incorporates the live movements of eye surface 69 withinthe decision process of adjusting the focal point of lens assembly 17,to within given tolerances. In this embodiment, the capture range foraxial acquisition is within +/−0.2 mm and tracking rates in excess of 40Hz are within the servo loop capability for maximum ranges on the orderof 2 mm.

Since mirrors and beam 64, 68, and 72, together with beam splittingcubes 65, 66 and 67, link the other assemblies of system 10 into acommon axial path passing through lens focusing assembly 17, they canall be referred to the lens assembly 17 as if the distance between lens17 and eye surface 69 were to remain constant. This is a majorsimplification in the manner in which eye surgery can be performed inthat the surgeon need no longer be continuously monitoring eye movementto verify a constantly changing focal position within the patient's eye.

For procedures where the targeted tissue layers lie posterior to thecornea, the surgeon/user will have the use of the parallax depth ranginginstrument 88, as shown in FIG. 4. This assembly relies on theintersection of two beams of light (from, e.g., a He—Ne illuminatorlaser) converging to a common point on a given surface. In oneembodiment, the parallax ranger allows mapping of a mesh of points,acquired through judicious adjustment of the zoom camera to shortdepth-of-focus (maximum magnification), which, along with correspondingvariation of the focus on the parallax ranger, produces a series ofdiffraction limited spots on the structures behind the cornea (iris,lens, etc.). In this manner, the resulting surface will define a desiredtemplate.

The inclusion of a parallax ranger within instrument 10 overcomesdifficulties commonly associated with specular reflection techniquesused for detection of the location and measurement of ocular features.Basically, only the tear surface layer overlying the corneal surfaceepithelium is usually detectable and measurable by specular lightreflection techniques. The reflected light signal is generallyinsufficient for the extraction of topographic information of theendothelium surface of the cornea (<0.02% reflection versus 4% from theepithelium), let alone for characterization of the three-dimensionalshape of the anterior and posterior capsules of the crystalline lens ofthe human eye. The parallax ranger unit provides the surgeon/user withthe option of using a combination of standard techniques which rely onimages of a target site. Thus, the surgeon/user can identify, to withinthe inherent error tolerances of the technique, when the instrument isfocused on a given surface. The precise focal point of the beam can thenbe varied by altering the incoming beam divergence by way of defocusinga beam expander means 22 (included within assembly 81). By redefiningthe origin of a given procedure to coincide with the depth at which theparallax ranger is focused on a surface, this new identified surfacebecomes the reference surface for performing a surgical procedure. Viathe user interface (See Sklar et al., U.S. Pat. No. 5,098,426 and U.S.patent application Ser. No. 475,657 (now abandoned), previouslyincorporated by reference), the surgeon/user can then define lesiontemplates or configurations to be performed at a given depth withrespect to the new identified surface.

Similarly, the motion of the eye along a plane perpendicular to theZ-axis of front focusing lens assembly 17 also needs to be stabilized.This is achieved using the X-Y tracking path shown in FIG. 5. Intrinsicto any tracking scheme is the choice of what is to be tracked. If theeye were a non-deformable body, then any landmark on or in the eye wouldsuffice for defining the motion of said material. However, the eyeneither moves nor deforms as a rigid body. Consequently, in order todefine the location of a moving tissue layer within the eye, thetracking landmark must be located contiguous to the targeted tissue andshould mechanically respond in a manner similar to the targeted issue.

For corneal refractive surgery, the eye limbus at the radially outwardedge of the cornea satisfies these constraints. It has the advantage ofnot only moving with the cornea—inasmuch as it is a part of thecornea—but, since it likewise is connected to the sclera, it will notrespond as dramatically to the transient deformations associated withthe microsurgery. In effect, pursuing the motions of the limbus willallow the computerized control system to replicate the template patternpresented on the display by the user interface, even though the eyesurface will be appreciably deforming during the course of the surgicalprocedure.

In one embodiment of the invention, the transverse X-Y tracking detectorconsists of high speed quadrant detectors and a microprocessor such thatupdated position information is fed to the tracking mirror atfrequencies substantially higher than the repetition rate of the laser,or the frame rate of the imaging camera. The response time of thetracking detector and processor should be sufficiently faster than themaximum repetition rate of the laser, so that laser firing can bedisabled, if necessary. The response time of the detector and processorshould also be higher than that of the driven tracking mirror, whichmust be capable of sufficiently high acceleration and velocity tocompensate for the fastest motion possible by the intended target.

In FIG. 5, light from limbus 70 passes through the objective lensassembly 17, is reflected by the X-Y tracking mirror assembly 72, and ispropagated via beam splitting cubes 65, 66 through viewing lens 63 to bereflected off beam splitter 67 to sensors of X-Y tracking assembly 85.In one preferred embodiment of the present invention, a spatiallysensitive sensor 50 comprising two quadrant detectors is used to trackan image of the outer rim (at the limbus) of the iris 32. As shown inFIG. 5A, the image of quadrant detectors (each with four quadrants 35,in this example) will then consist of a bright lune-shaped fieldcorresponding to sclera 33, adjacent to a darker field representing animage of the iris 32. The very dark central core which is an image ofpupil 34, is not captured by the detectors, as FIG. 5A illustrates,leaving a single sharp boundary to track. With various cells of thequadrant detector connected through differential amplifiers andnormalized by the sum, the resultant signals are sensitive only to theposition of the centroid of illumination of any of the above patterns.Quadrant detectors integrate the image illumination striking eachquarter of the detector face. The luminosity impingent on the detectorfaces will then generate voltage differences corresponding to theintegrated differences in light hitting the detector parts. A change inbackground light intensity will be ignored, as the increase across thefour (or eight) quadrants 35 of the detector face will remain the same.Voltage sums and differences among the quadrants serve to establish therelative direction of motion between two contiguous readings of thelimbus position. A shift in intensity at the sensor is thereby traced tomotion of the limbus. These dedicated quadrant detectors record voltagechanges extremely rapidly and can observe and quantify contrast changesand edge motions in less than 100 ms. In alternate embodiments,similarly fast but more sensitive position sensing detectors are used inthis application, yielding enhanced performance at even lower lightlevels.

The voltage change information is relayed to the computer controlassembly 16 wherein the actual coordinate shift is calculated. Controlassembly 16 then determines the angular corrections to be relayed to theX-Y tracking mirror assembly 72 and activates a voice coil or otherelectromagnetic drive assembly to pivot the orientation of mirror 72 soas to stabilize the X-Y motion of limbus 70 with respect to system 10.This embodiment of a tracking system uses entirely analog signals andtechniques to achieve tracking and can be made to work significantlymore rapidly than even the fastest involuntary motions of the eye.

In one preferred embodiment of the invention, the range of use, ortravel, is 2 mm in the X-Y plane. For ophthalmic applications, where theprincipal motions of the eye are rotations, it is often preferable todefine the range of use in terms of angular sweep of the eye. Forexample, an angular motion of the eye of 5° falls well within the domainof use of the X-Y tracking system. For a sighted human patient, it hasbeen estimated that such range of use will acquire an eye looking at animage point located in the far field (relative to the patient) andsituated along the optical axis of the apparatus.

The transducers of the tracking system adjust the position of the X-Ymirror along two rotational axes at accelerations on the target inexcess of 20 μm/ms for full amplitudes of over 2 mm, based onmicroprocessor-provided information relating to the new location of thesame tissue.

Eye surface 69 may be displaced in translation and/or by rotationalmotions centered on the globe of the eye; because the X-Y trackingmirror 72 rotates about a point within its assembly that is differentfrom the eye's center of rotation, a desired change in X-Y trackingmirror position also requires a correction of the X-Y axis position ofthe depth ranging and tracking assembly 84. Consequently, the algorithmwhich pivots the X-Y tracking mirror 72 along paths 61 and 62, also mustrelay instructions to the computerized control system to adjust thedepth tracking and ranging assembly 84 so as to maintain the correctorientation. The preferred methods to achieve this correction use acompensating mirror 60 within the Z-tracking assembly (not shown in FIG.5).

The tracking system has the advantage of being able to find an absoluteposition of the target even after a temporary loss of tracking. Forexample, if a surgical procedure is in process and an obstacle, such asa blinking eyelid in many ophthalmic procedures, interposes the trackingimage such that the procedure is interrupted or temporarily aborted, thetracking system will automatically store in memory the last position inthe firing sequence so that once the target is again reacquired, theexact location of the next point in the firing sequence can bedetermined automatically and the servo mirror be repositionedaccordingly.

FIG. 6 shows the surgical microscope loop. This subassembly includes thelow-level-light camera and the zoom optics. The camera preferablycomprises an intensified video camera, for example a silicon intensifiedtarget (SIT) tube camera. Alternatively, it can be a conventional videocamera in combination with a microchannel-plate intensifier. In eitherevent the camera's sensitivity preferably is about 1000 times that of anormal video camera, enabling the system to look at weakly scatteredlight and targets poorly illuminated for the desired levels of highmagnification at large working distances.

In a preferred embodiment of the present invention, the system uses acombination of specular and scattered light techniques for detecting andidentifying diffusely reflecting surfaces, specularly reflectingsurfaces, surface displacements, features, and shapes of the patient'stissue. This is particularly useful in the eye where it can provedifficult to differentiate between the amorphous tear layer anterior tothe cornea and the structured epithelial surface layer of the cornea.Even the cell walls of the endothelial cells of the cornea or of theanterior lens capsule will scatter light. The intensified surgicalmicroscope can produce an image of these actual cells by forming animage composed by detecting scattered light. The surgical microscope, aswell as the tracking camera, can substantially exclude specularlyreflected light by cross polarization of selectively polarizedilluminators. Other methods for reducing specular reflectionspreferentially to scattered images are also possible.

The microscope optics are designed to provide flat field, anastigmatic,achromatic, nearly diffraction limited imaging with opticalmagnification zoomable approximately over a 15-fold range of, say15×-200×. The magnification is adjustable and is typically selected tocorrespond to the largest magnification which can still be comfortablyused for situating a lesion (that is, the smallest field of view whichcan be used when magnified across the fixed display size of the videomonitor.) For example, for corneal refractive surgery, where the surgeonneeds to observe the cornea from limbus to limbus, this corresponds to afield of view of approximately 12 to 14 mm. At the screen, the zoomoptics allow for adjustable magnification in the range of about15×-200×, for example. This enables the surgeon to view a very narrowfield, on the order of a millimeter in width, or a much wider field atlesser magnification. This is useful in enabling the surgeon to assurehimself that he is aimed and focused at a particular desired region.Zooming can be effective through use of a joystick, trackball, mouse, orother pointing device 42 to access a scroll bar in the user interface.

The function of the viewing mirror 68 shown in FIG. 6 is to move thesurgical microscope image on the screen to the left or right or up ordown, independent of the aiming of any other subsystem.

FIG. 7 shows the light path for the topography assembly 98, whichprovides a three-dimensional mapping system directed at the surface ofthe target, e.g., the eye of the patient. In a preferred embodiment ofthe system 10 (as described by Sklar in U.S. Pat. No. 5,054,907 andfurther extended by McMillan and Sklar in U.S. Pat. No. 5,170,193, allof which are incorporated herein by reference), the subassembly 98 maycomprise a light projector 95 including an internal profilometry source90, an illumination mask 96, an optical collection system 94 and aprofilometry assembly consisting of, e.g., an adjustable aperture 99 anda CCD camera 97 equipped with a frame grabber, such as an array of dotsarranged into rings and radial spokes converging to a common center,onto the tear layer of the eye. The reflected images of thepredetermined pattern are collected by the optical assembly 94, whichmay include a set of plates to correct for any astigmatism induce by thetracking mirror 72 and any other interior mirrors, fed into theprofilometer camera 97 through the aperture 99 for analysis. Bycontrolling the angle of acceptance of the light bundle from eachvirtual image, the adjustable aperture acts as a spatial filter,providing a physical representation of the source of paraxial raysthrough trade-offs between resolution and brightness. The cameraincludes mans to digitize and electronically enhance the images. Thesignals are fed to a microprocessor which performs preliminarydisplacement analysis using software means (embedded within controller16) based on mathematical morphological transformations as described bythe '193 patent. The transformations comprise a solution of a set ofcoupled differential equations, whereby the local normals and curvatureparameters are computed at each data point so that the surface can becomputed to within the measurement accuracy, and subsequently displayedon the video screen 20. The methods of light projection and profilometrypermit the system 10 to operate with low intensity light signals toenhance safety and patient comfort while extracting significant signallevels form the noise background.

In other embodiments of the profilometry assembly, alternativeprojection techniques may be utilized in place of or in addition to themapping and projection means described above. In one embodiment, anexternal profilometry source 89, consisting of an array of LEDs projectsa patter of dots onto the eye in a manner described by McMillan et al.in U.S. Pat. No. 5,283,598. In this embodiment, curvature measurementsof the anterior surface of the cornea can be obtained extending up to 8mm in diameter around the center. Other techniques based on off-axisillumination may utilize, e.g., a slit lamp illuminator 77 to obtainmeasurements of the thickness of the cornea, the depth of the anteriorchamber and/or the thickness of the lens (the latter coupled withstandard keratoscopy methods to correct for corneal curvature). Mountingthe slit lamp at a fixed location relative to a CCD camera (such as 97)and rotating the entire structure around a center axis would alsoprovide a method to collect global corneal data (out to the limbus) yetwithout sacrificing local accuracies, given the simultaneous 3D trackingcapability already contained in the system. In this manner, the domainof topographic measurements can be extended from limbus to limbus whileproviding pachometry data as well. Alternatively, topography methodsbased on Ronchi grating in conjunction with Moire interferometry, oradvanced holographic techniques as discussed by e.g., Varner (inHolographic Nondestructive Testing, Academic Press, New York, 1974 pp.105) and by Bores (in “Proceedings of Ophthalmic Technologies,” SPIE1423, C. A. Puliafito, ed., pp. 28 (1991)) may be utilized in futureembodiments of system 10, if warranted for specific interventions.

FIG. 8 is a schematic optical layout of a preferred system of optics forthe instrument of the invention. In FIG. 8, a Schneider Cinelux Ultra 90mm focal length f/2 lens is combined with a Schneider Tele-Xenar 360 mmfocal length f/5.6 lens, matching conjugates to form a 4×/0.24 numericalaperture (N.A.) “objective lens” 17 with a working distance of 59 mm.This type of design embodies a key feature of the present invention,whereby a comfortable distance between the patient and the optics isimplemented (sufficient to provide the surgeon/user enough open clearspace to easily fit his hands between the front “objective lens” 17 andthe patient's eye/target surface 69) while maximizing the aperture ratioof the system. A beam splitter between the front and back lenses of this“objective lens” allows the 90 mm lens to also serve as the finalfocusing lens for the laser. A Schneider Xenon f/2 lens, with 28 mmfocal length, relays the image to the camera contained withinsubassembly 86, with magnifications zoomable from about 0.4×-5.4× inthis embodiment of the invention. An appropriate field lens 58 is usedto provide uniform illumination across the image of the maximum 15 mmfield of view at the object (eye) and to reduce the magnification.Zooming can be accomplished by computer-and-stepped motions of both thezoom lens 59 and the camera. The total optical magnification is thuszoomable in this embodiment from about 0.8 to 11. With the imageincident on a ⅔″ video detector and displayed on a 13″ (diagonal)monitor, an additional 19× video magnification is gained, thus a maximummagnification from the target to the screen of about 200× is achieved.

Another important feature of the optics of the system of the inventionis that the servo tracking mirror 72 actually is positioned inside the“objective lens” assembly (the final element has been designed to havesufficient field to accommodate the small misalignments caused by thetracking mirror). This enables the system to achieve rapid tracking ofocular features (or other tissue features) in an efficient andrelatively simple assembly, without moving an entire objective lens infollowing the sometimes rapidly moving features.

The optical system is designed without correction for the aberrations ofthe eye. For work in the cornea no corrections are needed. For work atimage planes located posteriorly to the cornea, such as the retina, forexample, contact lenses 28 (e.g., Goldman or similar) may be used, asshown in Inset a of FIG. 8.

As illustrated in FIG. 8, the illuminator light beam contained withinassembly 82, first is reflected off a turning mirror 73, thentransmitted through mirror 64, to join substantially coaxially with thepath of the laser beam along the beam axis (see FIG. 2). Both beams arethen steered through the beam steering and aiming optics in assembly 81and are reflected off a reflective surface in the polarizing beamsplitter 65 before being incident the tracking mirror 72. The polarizingbeam splitter 65 (along with beam splitter 67) effectively preventinternal back reflections of the laser pulses from the optics of thesystem from damaging or overwhelming the sensitive video microscopecamera contained in assembly 86.

Also indicated in FIG. 8 are the optical tracking and viewing elements,namely, depth ranging assembly 84, X-Y tracking assembly 85, andsurgical microscope 86, all share the same optical path from beamsplitter 66 to the eye. Some key design details of the Z-trackingassembly 84, including the illumination source (such as a red Ne—Nelaser) are shown in Insert b. These are described in more detail in U.S.Pat. No. 5,162,641.

As FIG. 8 shows, the beam generated by the therapeutic laser 86 andparallax ranger 82 are coaxial with each other, but the axis of thesebeams is not necessarily coaxial with the axis of view of theprofilometer camera 97, the topography illumination source 90 or theother tracking/viewing assemblies 84, 85 and 86. This is because ofdirectional steering Risley prism sets 21 embedded within assembly 81which are outside the optical path of assemblies 84, 85 and 86, butwithin the optical path of the parallax depth ranger 82 and laser 87.The Risley prisms are steerible via the computerized control assembly 16under the control of the surgeon/user through user interface commands.They provide means for adjusting about the X and Y axis, thus lettingthe physician select different locations for firing the laser, asdisclosed by Fountain & Knopp in U.S. Pat. No. 5,391,165 (which claimspriority from U.S. patent application Ser. No. 07/571,244). Elements 82and 87, therefore, will only be coincident with the axis of view ofdepth tracking assembly 84 when the surgeon aims the laser directly atthe center of the field of view of assembly 84. In other instances theywill share the same “optical path” via elements 72 and 17, but they willnot be on identical axes. The Risley prisms within assembly 81 allowmovement of the actual aim of the therapeutic laser beam from laser 87to a real aiming point which is coincident with the computer-generatedaiming points.

The set of beam expander lenses 23 preferably are positioned as close aspractical to final objective lens 17, and are initially adjusted so asto expand the diameter of the laser pulse emerging from the laser cavityand collimate it so that a parallel but expanded beam of light emergesfrom lens 22. The expanded, collimated beam is incident upon the finallens 17, and the expanded beam fills the lens to the extent compatiblewith vignetting for off-axis aiming. thus, a large diameter beam isfocused by lens 17, so that only at the point of focus within the eye isthe diffraction limited pulsed laser beam effective in generating thedesired therapeutic lesions in the eye. The depth of the focal point isvaried by adjusting the distance between the two lenses 23, which hasthe effect of changing the degree of collimation and hence the focus asindicated explicitly in FIG. 8. the surgeon's adjustments of the focusof the beam via the computerized control system 16, are superimposed ontop of the automatic adjustments effected by the tracking system, andnet focus changes are carried out by the system. This is easilyaccomplished using hardware and software associated with the systemwhich does not in itself form a part of the present invention.

The decoupling of the aiming and viewing functions allows off-axis work,which represents a major improvement in the function of the system 10,in that off-axis capability is a mandatory feature for corneal and mostother applications. Thus, an independent mirror 68 is inserted upstreamof assembly 86 to allow viewing, while aiming is performed independentlyin the coaxial illumination path using the Risley prisms 21 ofsubassembly 81. In an alternative embodiment of the system disclosedherein, a secondary angular steering mirror 60 (no explicitly shown inFIG. 8) may be added in assembly 84, to compensate for motion impartedby the X-Y tracking mirror which can, for large enough eye motions,cause the Z-tracking system to “lose lock.”

Inset c of FIG. 8 shows some schematic detail of the external slit lampilluminator, provided in an alternative embodiment of system 10 toaugment and/or replace the internal profilometry illumination source 90,and provide ocular thickness measurements as was described above (seediscussing following FIG. 7). The slit lamp constitutes the only elementof the system not coaxial with the optical path defined by the trackingmirror 72 and the “objective lens” 17 common to all the othersubassemblies.

FIGS. 9 a, 9 b, and 9 c show three perspectives of an ergonomicrendition of the workstation which incorporates the entire system 10.System 10 in this illustrated embodiment of the invention is intendedfor ophthalmic surgery, with the patient to be seated, as shown in FIG.9 a, in a chair 11 with his forehead against a forehead rest 12 and hischin against a chin rest 13, as shown in FIG. 9 b. Both forehead andchin rests are fully adjustable. The surgeon/user is free to stand at aconvenient location where he/she can survey the progress of the surgeryas depicted on the video monitor means 18 (containing the video displaymeans 27, including screen 20) as depicted in FIG. 9 c, while havingdirect access and observation of the patient, or to sit in a chair 14.The seats 11 and 14 for the patient and the surgeon, respectively,preferably are fully adjustable with e.g., tracks 15 (shown in FIG. 9 a)for adjusting proximity to the apparatus and with full height and seatback adjustability.

A hand held system control switch 24 in FIG. 9 a may be provided for thesurgeon/user as a safety device which will both enable the lasertriggering means when sufficient pressure is exerted on device 20 (via asimple toggle switch, for example), or alternatively will immediatelyinterrupt laser firing if pressure on the control means 24 is released.

FIG. 10 is a functional block diagram showing the principal componentsand individual control and informational feedback functions of theprecision laser surgery system of the invention, all indicated as beingunder control of a central processing computer 16, designed to integrateand control the operation of the entire system 10. The computer mayinclude a microprocessor 140, software programs 141, and firmware 142,as indicated in FIG. 10, as well as a number of other control andindicate features (not indicated) such as the enabling (or disabling) ofinternal safety interrupts, a light-emitting diode (LED) display whichindicates when the tracking system and target acquisition system areoperational and on-target, an LED which lights up when the systemcomponents have successfully been verified to be performing withinsystem specification ranges, an LED indicating power is on, and adedicated video display function to assist in detecting location of asystem malfunction. Note that some key functions in the system arecarried through dedicated microprocessors 150, which, for simplicity,are shown in FIG. 10 sharing the same block as the centralmicroprocessor 140.

During the start-up phase of system 10, a complete system verificationis performed automatically without further prompting form thesurgeon/user, including a set of internal diagnostics listing the statusof operational use of the various assemblies. During this start-upphase, the assemblies shown in FIG. 10 (and FIG. 1) are eachindividually tested for operational status within prescribed tolerances.If all tolerance levels are satisfied, the user interface screen 20appears and the system is enabled for use. Additional safety LEDsacknowledge sufficient pressure on the laser fire safety interlock inthe hand-held (or, foot pedal) safety device 24, and whether themicroprocessor generated template pattern is in control of the firingsequence.

As shown in FIG. 10, the central computer (which receives simultaneousdiagnostic measurement and tracking information) closes each controlloop through a central fire control function shown as block 100 forminga critical part of the computer control assembly 16. This fail-safemechanism is a key feature provide within the instrument and system 10.Thus, the computer, which directly controls laser firing, as indicatedby control line 144, automatically interrupts the firing sequence shouldany of the required operational specifications not be met (such as lossof tracking, deviation of the pulse energy, etc.). If all presetconditions are met, the computer control assembly enables and fires thesurgical laser in accordance with preselected templates shown,functionally, as block 6. The required information comprisesconfirmation that the template is still positioned correctly, i.e., thatthe targeted feature of the eye has been tracked within a preselectedtime allotted, so that the images of the eye remain stabilized. If thisconfirmation is not sent (or a contrary signal could be sent signal thattracking is lost), the template controlled laser firing is immediatelyinterrupted, as discussed in more detail below.

The user interface shown in a block 19 in FIG. 10, communicates with thecentral computer unit 16 as indicated by control line 123, though it mayalso have some controls which do not involve the main microprocessor140. Thus, if the surgeon wishes to generate a template for surgery, asshown in dashed line 131, or merely to change the display on the videoscreen for the purpose of selecting a different type of presentation, orfor imposing a different surgical path on the screen, thesecommunications are carried out through the central processor unit (CPU)140 (taken to include appropriate software 141 and firmware 142), whichcontrols the computer-generated images (CGI) on the screen as well asmost other functions in the system. As such, once the surgeon/user hasfinally determined his selection of template, has superimposed thattemplate using the computer controls 16 onto the positioning diagnosticsat the desired location where the surgery is to be effected, and themodifications to the shape of the template have been effected toaccommodate for the particular configuration of the patient as observedthrough the video display means 27 (which includes screen 20) and thereconstructed target cross-sections, then the system is set toautomatically fire at a discretized approximation of the configurationselected on the video screen 20. Discretization techniques, computerpattern overlay means, and the inherent CAD/CAM software techniquesnecessary to accomplish this process are known art and, as such, are notfurther described. The user's control of the template is thus indirect,proceeding via instructions received and stored in the computer memory,which in turn, generates, processes and stores template information asshown by control line 121.

The CPU 140 is connected to a number of other components. For example,it can send information to an I/O unite (not shown in FIG. 10) forrecord keeping. The transmissions may include, for example, patienthistory records to be printed or stored.

The CPU 140 can send control signals to a dedicated I/O boards 152 whichmay be used for e.g., driving motors associated with the steering Risleyassembly 21, as well as for driving X-Y axis adjustments and othertracking functions through software included in 151. Commerciallyavailable dedicated I/O boards are capable of handling 16 analogchannels and three digital channels in the currently describedembodiment of the system 10. Thus, one board (in, e.g., 142) can handlediagnostic information relating to laser status, position status,tracker mirror status, and other diagnostics which may be implemented asneeded such as intraocular temperature, intraocular pressure readings,and surface wave propagation measurements to enable calculation of theYoung's modulus and other elasticity constants in an effort to determineapplicable constitutive relations. The sensors for these conditions ofthe eye are not shown in the drawings, but can be incorporated in thesystem of the invention.

In FIG. 10, the surgeon/user is indicated at 8. Interaction between thesurgeon and the patient is mostly indirect (as shown by dashed line 5),via the instrument and system of the invention. Thus, information anddata concerning the patient's tissue is fed back, indirectly, throughthe instrument, to the surgeon, via video display 27, contained withinuser interface 19. The surgeon/user inputs instructions and commands touser interface 19 and the user interface feeds back information to theuser, principally via video screen 20. This is indicated by a line 25.

The pointing device 42 is indicated in FIG. 10 as a key link in thesurgeon's control of the user interface. It is used to control allaspects of the operation from generating templates to viewing,diagnosing and treating the target tissue.

The eye/target 3 is shown as sending information to a topography system98 (comprising a light projector 95 and topographic data collectionsystem 77), a viewing/imaging system 86 (comprising blocks 45 through49), and to X-Y and Z position analysis tracking detectors 50 and 53contained within assemblies 85 and 84, respectively. As represented inFIG. 10, the imaging/viewing system 86 comprises the video microscope46, which presents the tissue video image (exemplified in FIGS. 12-15discussed below), the zoom control 47, the aiming viewing means 48 andthe focus viewing means 49. A double-ended arrow 127 indicatestransmission of the video information to video display means 27, forminga part of the user interface 19, and resulting in live video images 4 onvideo screen 20. Control arrow 127 between the user interface andviewing system 86 also indicates that the surgeon may control themagnification of the video microscope depicted in block 46 via zoomcontrol function 47, as well as view selected aim points and beam focus,all of which comprise parts of complete assembly 86.

The control line 123 from the user interface to the microprocessor(which indicates the surgeon/user's selections made by input controlsother than touch screen), thus serves to represent another user input tothe microprocessor 140 active when the user steers the field of visionand the aim of the laser. Such deliberate control by the surgeon willindirectly control the laser beam aiming and focus via themicroprocessor (along the control lines 113 and 114, as discussedbelow). User interface signals to the computer control are also used bythe CPU 140 to adjust the CGIs accordingly, reflecting precisely thedesired change in beam focus, image magnification and aim points.

The content of signals sent by the microprocessor (CPU) 140 to the videoscreen (along control line 123) relate also to the computer-generatedtopographical images acquired as shown by line 101 from topographysystem 98, and discussed further below. CPU 140 also controls thedisplay of the branching look-up tables 30 shown on screen 20, as wellas other pull-down menus, displays and other pertinent information.

In FIG. 10, information about eye 3 is shown as being sent to a block 77labeled Topography via control line 104. Arrow 102 indicated thederivation of such information from the eye via the projection system 95while the transformation and processing of said information by thetopography system 77 is represented by arrow 103. An information controlline 101 indicates processing and feedback via the computer controlassembly 16 and dedicated microprocessors contained in 150. Block 77 istaken to include the sensors, CCD cameras, such as profilometer camera97, optical collection assembly 94, aperture 99 and analysis loops. Asrepresented in FIG. 10, the functions of a dedicated microprocessor andprogramming for this subsystem are included within blocks 150 and 151,respectively. The derived information relating to the topography of theeye tissues is then sent to the tracking stabilization blocks discussednext.

The X-Y position analysis and tracking system (contained within assembly85 and described operationally for FIG. 5) proceeds primarily throughthe tracking detectors 50 and the servo drive 51, but is also understoodto include the servo logic loops and any associated optics required tosteer the light emanating from the images received from target/eye 3, asindicated by arrow 108, for the said purpose of detecting and followingany movement of the patient's tissue. This information is related to theX-Y servo drive 51, via information control loop 109 which, in turn,controls the tracking mirror 72, as indicated by arrow 116. This logicsequence indicates that the detectors subsystem, after analyzing theimages and determining that a feature has moved, sends information orinstructions to the servo drive, which constitutes the target trackingassembly (along with dedicated processors included in 150). Theinformation or instructions can comprise new coordinates for theposition of mirror 72. The target tracking assembly thus translates thenew coordinates into instructions for the mirror drivers via arrow 116to the servo mirror 72), which instructions may include coordinatetransform information and commands for the tracking mirror 72 to turn toa new angle which will again be centered on the same features.

An information arrow 111, shown between the position analysis trackingdetectors and the computer control 16, indicates processing of theinformation and stabilization of the video images by a dedicatedmicroprocessor, contained within the units 150, shown in FIG. 10 (forsimplicity) as embedded within the central computer assembly 16.Computer processing functions relating to the X-Y tracking unit includeappropriate programming units which are able to analyze data taken bythe tracking detectors 50 and to determine form the data when featureshave moved and to relocate those features and calculate new coordinatesfor mirror position. Some of these functions were described further withreference to FIG. 5. Control arrow 117 also represents feedback from themirror assemblies as to their actual position, as well as confirmationthat the mirror was physically moved, i.e., that the instruction to themirror resulted, where indicated, in a physical displacement. If thismove does not occur, the system loops back to the target trackingassembly which sends a signal along control loop 144 to disable thelaser firing. The important control arrow 144 thus relates to thepreferred safety feature embodied within the present invention. Thetarget tracking assembly, if unable to track the moved feature to a newlocation within the time allotted (which may be as fast as a fewmilliseconds in a preferred embodiment), will send an instruction to aninternal fire control 100 to abort firing of the laser, and this commandis relayed to the laser power control via arrow 144. The automaticfiring control mechanism represented by block 100 will also interruptthe execution of the template program, vis a vis the control line 121 inFIG. 10. The interrupt preferably lasts only until the feature isrecovered via the tracking loop (discussed above), if in fact thefeature is recovered.

Examples of tracking loss not associated with the logic loop are failureof the signal to be effected by the servo drivers, required mirrormotion exceeding the limiting displacement of the servo driven actuatorsand malfunction of the drivers or slides. Safety controls which shutdown the operation of the system whenever tracking is lost are a featureof the present embodiment of the invention but are not further describedas they comprise standard safety devices known in the field.

In one embodiment of the invention, a microprocessor in block 150 alsocontrols the tracking mirror or servo mirror 72, as indicated by arrow117. The microprocessor controls the mirror in response to input fromthe tracking detectors 50 in conjunction with suitable programmingfirmware and software 152 and 151, respectively. Thus, once the trackingdetectors input signals to the microprocessor (via control line 111)which indicate that the subject tissue has undergone movement, themicroprocessor handles the position analysis and the target tracking(mirror instruction) and outputs as signal in response to the results ofthe tracking to the tracking mirror 72 as indicated by line 117.

A dashed control 120 from servo tracking mirror 72 to laser aim block 75indicates that the laser aim is steered along with the X-Y tracking (asdiscussed in reference to FIG. 4). In a preferred embodiment, there maybe an additional control line (not shown in FIG. 10) from the trackingmirror to the viewing assembly 86 to allow for the fact that since thelaser and surgical microscope lines of sight are not coaxial, the fieldof tissue being viewed and the laser are always decoupled.

It is noted that the dedicated microprocessor or other logic unit havingthe capability of carrying out the logic sequence needed for patternrecognition, coordinate transform analysis and generating instructionsto the mirror drivers to appropriately adjust the X-Y position of themirror 72 can also be included within the servo drive 51, in which casethe function of the separate control arrow 11 is obviated.

Similarly, the Z-tracking detectors 53 (contained within the depthtracking assembly 84 discussed earlier in connection with FIG. 3) sendcommands regarding viewing depth and beam focus to a Z servo drive viacontrol loop 106, which in turn relays the information to the finalfocusing lens 17 via information loop 105. In a preferred embodiment ofthe invention, the change in orientation of the tracking mirror 72 iscommunicated to the Z-tracking compensator mirror 60 via control loop130. This feature is provided to maintain the focus of the Z-trackingsystem on the instantaneous vertex of the cornea, as discussed abovewith reference to FIG. 8.

We note that the final focusing lens also forms apart of the imagingsystem 86, in the sense that the surgical microscope receives light on apath which passes through this lens 17, and the focus of the imaging isadjustable at 48 and 49 by the surgeon/user; consequently, no separatecontrol line leading from the objective lens to the viewing assembly isindicated in FIG. 10.

The user interface activated laser fire control is shown by line 144with arrowhead toward block 44 representing an internal laser firecontrol mechanism which turns on the power source 44 that acts as thedriver for the therapeutic laser 87. The fire control sequence isinitiated by the surgeon/user when clicking the mouse 42 which moves acursor across the video screen. Firing can be manually interrupted bypushing the “abort” button 24, provided as an additional safety featurethat is under control of the surgeon/user as indicated in FIG. 10 bydashed line 125.

When operating, a fraction of the beam passes through a laser diagnosticassembly 74, as shown by control line 129 which serves the purpose ofmonitoring the laser pulse energy to insure it is performing tospecification. The information is relayed to the central computer unit16 to be analyzed and compared with specific parameters, as indicated byline 112.

The laser beam also passes through the steering and aiming subassembliesshown as blocks 75 and 76 (contained within subassembly 81). Thesteering assembly 75 includes the Risley prisms, which are not under thedirect control of the surgeon. The beam focusing assembly includes beamexpander 22, which is likewise not under the direct control of thesurgeon. Note that the entire beam steering, aiming and positioning loopalso includes the front objective element 17 as was discussed vis-à-visFIG. 4. So, again there is no separate control indicated between theobjective lens and the beam steering and focusing blocks 75 and 76.Instead, these subsystems are shown as receiving direct controlinstructions form the central microprocessor via control lines 113 and114 (which include indirect information relayed through the trackingmirror 72 and objective lens 17, both of which are adjusted viaappropriate servo drives whenever the patient's target tissue moves).

Finally, the dashed line 5 indicates the laser beam's action on thetarget, i.e., the patient; the actual laser treatment is thus onlyindirectly controlled by the surgeon/user.

FIG. 11 shows again separate functional blocks for the target viewingassembly, the target tracking assembly, the topography assembly, thebeam positioning/aiming assembly and the fire control, all shown now asbeing activated by the user interface, which is in turn manipulated bythe surgeon/user through a suitable pointing device 42 also indicated inFIG. 11. The operator/user interface interaction takes place primarilythrough the video screen means 20 (and associated elements such as thepointing device 42) as indicated by control line 25, while centralmicroprocessor control of the interface is shown by line 123. The userinterface 19 comprises for the most part an “intelligent” menu ofoptions available to the surgeon, the video screen 20 which displays theoptions in a suitable number of modules, the pointing device 42 (such asa mouse, joystick, trackball, light pen, etc.) for making selectionsfrom the menu, the fire control (or “abort”) button 24 and various otherbuttons and numerical displays as were indicated in FIG. 9 c in front ofthe surgeon/user. Aside from the safety feature indicators discussedpreviously, the trackball 42 (or other pointing device, as mentionedabove) enables the surgeon/user to control and select from among thevarious software options available for a given mode of operation.Rotation of the trackball controls the position of a cursor on the videoscreen. A button next to the ball enables special features on the screenand allows the user to superimpose the proposed therapy on the videogenerated images of the target tissue. In the present invention,commercially available computer graphics software packages form aportion of the basis for providing the surgeon/user access to definingsurgical templates. Other buttons allow the surgeon/user to switch fromselecting previously defined templates, to modifying or creating newtemplates.

With the user interface, the surgeon is able to make selections as totypes of surgery or templates to be used in the surgery, to viewdifferent portions of the tissue, to aim the laser, including the depthat which the laser fires, and to fire the laser to execute apre-programmed sequence of firings. It also enables the surgeon/user tointerrupt the procedure at any time. The surgeon makes his selections bymoving a cursor across a Windows menu consisting of several modules eachcontaining a number of options that can be displayed in the form of abranching look-up table 30 and pull-down menus. The cursor ismanipulated, preferably by (in order to obviate the risks of miskeyingon a keyboard) the pointing device 42 alluded to above. The symbols inthe menu will include the type of display desired for the screen asshown in the examples displayed in FIGS. 12-15; selection of templatesfrom among pre-programmed patterns for the proposed surgical procedure;other surgical parameters such as the laser pulse power level or therepetition rate of the laser beam; the beginning and ending diopterpower of the corneal “lens” or, more generally, the opticalprescription; the shape of the lesions; modifications of the templatesor creation of new templates, memory storage and retrieval ofinformation; record keeping and access to patient history files; accessto statistical information about the likely outcome of a proposedsurgical procedure; a selection of levels within the eye for whichinformation is desired for a given surgical procedure; and others.

All of the above operational functions are created through softwareprogramming, the details of which do not in themselves form a part ofthe invention and are within the skill of the programmer.

As shown in FIG. 11, the surgeon/user starts the procedure by generatinga template (or a set of templates), a function indicated in block 131.Based on a set of pre-programming patterns, the patient's opticalprescription or—in the case of controlled animal studies—actualtemplates for the proposed procedure (derived from other previoussurgeries conducted by himself or by other surgeon and stored inmemory), means are provided for the surgeon to create a new template ormodify an old template by appropriate resizing and rescaling. The listof pre-stored patterns may include geometric shapes such as annuli,arcs, boxes, ellipses, radii, and others, as shown in the pull-down menu36 of FIG. 12, under the “utilities” module 31. Specific types ofoperations and/or lesions may be selected from among options storedunder the “treatment” module shown as vertical box 37 in FIG. 13. Forexample, in the case of corneal surgery, the starting point forgenerating templates for a particular eye segment may consist ofselection from among a collection of relevant lesions, such astangential (T-cut) or, for radial keratotomy, radial (2-rad, 4-rad,etc.), as illustrated in vertical box 38 of FIG. 13. Different sets ofpatterns are provided for e.g., cataract surgery, posterior eye segmentsurgery, or other forms of intervention for which the system of thepresent invention is deemed appropriate. Specific shapes of lesions cantherefore be selected by the surgeon such as, e.g., the screens as shownin FIGS. 12 and 14 for corneal surgery, or a different set of screensfor cataract surgery, or yet a different set of screens for posterioreye segment procedures. In a preferred embodiment of the display,templates are drawn on the screen in three-dimensions through selectionfrom several standard geometrical shapes as shown in FIG. 12.Alternatively, a free form option may be included to allow thesurgeon/user to draw arbitrary shapes as may be appropriate for certaintypes of surgical procedures. Selection of a treatment plane can also bedone through, e.g., an “orientation” menu, indicated in box 37 of FIG.13, under the “treatment” module. The selected patterns can then be usedas depicted or, if a closed curve is indicated, filled in automaticallyaccording to the prescribed distance between firing locations asindicated in the menu selection under e.g., the “set parameters” box 39illustrated in FIG. 14, and contained in the “treatment” module 37depicted in FIG. 13.

The patterns selected are superimposed on a grid, shown on the screen,with spacings corresponding to appropriate dimensions within the eye.For example, in the case of corneal surgery, a 10×10 grid with 1 mmspacings would adequately describe the human cornea (which has adiameter of 12 mm). The areas between the grid points are transparent tothe treatment beam.

When pre-programmed templates of the surgical path to be followed areused, such as in controlled animal studies, the surgeon has access tothe same options as indicated above, in addition to superimposingdirectly the template on the screen over the ocular tissues.

Access to magnification is provided throughout the template selectionand diagnostics phase through a zoom option, located on the screen. Thisfunction is within the domain of the viewing/imaging assembly and isindicated as block 138 in FIG. 11. The surgeon can thus view any desiredsegment of the treated area and/or the shape of the proposed lesions, atvarying magnifications up to the limit imposed by the hardware.

The first step in the surgical procedure involves patient eyediagnostics, including key topographic measurements such a provided byprofilometry, keratometry, and corneoscopy as indicated by block 132 ofFIG. 11. A “diagnostic” module may be provided in a preferred embodimentof the user interface, an example of which is shown in FIG. 15. Thismodule may comprise commands to perform various non-invasive proceduresand present the results in the form of three-dimensional graphics andrefractive power maps. Controls of the viewing system and the tools forperforming measurements may all be exercised concurrently within thismodule. Thus, profilometry measurements, which involve the topographysubassembly 98, provide the surgeon with data on the patient's cornealsurface. The procedure involves projection of a pre-selected patternunto the eye or other alternative techniques as was discussed for FIG.7.

In a preferred embodiment of the invention, the 16-spoke, 5-ring patternshown in FIGS. 12 and 14, has been selected, although other patterns maybe appropriate for different procedures. The reflected images aregrabbed, digitized and spatially transformed to reproduce key surfacecharacteristics, which are saved as a file on a disk. The keratometrymeans reads from the file to generate a 3D surface that can be displayedon the screen in the form of a contour map as part of the corneoscopyroutine, once the appropriate radii and planes have been selected. Anexample of such a power map is also shown in FIG. 15. In one embodimentof the software, a 75×75 matrix is used to generate the surfaceprojection, in the form of e.g., an equi-power map 92. The 3D patterncan be manipulated by means of a scroll bar to rotate and tilt it. Itcan also be displayed in the form of a color coded contour map as visualaid to indicate feature elevation. A palette is provided in the menuunder e.g., the “utilities” module to allow color selection for thedisplay.

Based upon the corneal measurements, the spatial map of the refractivepower of the cornea can also be constructed. This may also be includedin the diagnostics module, and the power map can be presented in aseparate window, if desired.

As discussed above, FIGS. 12-15 show examples of what may be displayedon a screen 20 of the video monitor 18. The information on the screen 20is intended to give the user a full range of information regarding thethree-dimensional structure or features of the particular tissues onwhich laser surgical procedures are to be performed. In a preferredembodiment of the user interface, some symbols are included on thescreen such a in vertical strips 31, 36, 37, 38, 39, and 40 as shown onthe screens of FIGS. 12, 13, 14, and 15. These symbols comprise a menuof selections for the surgeon/user. Other display means can be also usedto present data in a more easily understood manner to the surgeon/user.For example, in FIG. 15, a preferred embodiment of the graphicalrepresentation means 92 or the topographical map means 93, is shown in asuper-posed manner. These can also be shown as separate windows. Themenu 40, shown in FIG. 13, may be used to generate on the video screento show pertinent measurement data relating to the tissue on whichsurgery is to be performed. A final selection of the reference surfaceat a given target depth can be made concurrently with the diagnosticroutine, by entering appropriate data in box 39 of FIG. 14 (whichcorresponds, in the example of FIG. 13, to the “set parameters” menu,shown as part of the “treatment” module 37) and observing the immediateeffect on the reconstructed corneal surface, displayed in a mannersimilar to the example shown in FIG. 15. This type of corneoscopydisplay provides critical aid to the surgeon in determining, e.g., thedegree of astigmatism present in the patient's tissue. In the preferredembodiment, the user will also be able to superimpose the template ofthe selected surgical path on the video microscope-generated image ofthe corneal (or other tissue).

A key step in the treatment involves selection of laser operatingparameters for the actual surgery, indicated by block 133 in FIG. 11 andillustrated in the photograph of the user interface, as depicted in box39 of FIG. 14. The principal parameters included in the treatment modulemay include the energy of the laser, the repetition rate, desiredspacing between fire points, desired lesion depth and thickness (for thesurface selected earlier), direction of treatment along the Z-axis(inward, outward), lesion radius for selected profile projections, andother pertinent parameters as may be indicated by a particular type ofsurgery to be performed. FIGS. 12 and 14 also show examples of what maybe indicated on the screen for a selected corneal lesion shape which isshown in two projections, customarily referred to as S-1(superior-inferior) and N-T (nasal-temporal). In a preferred embodimento the elements included in system 10, the maximum energy/pulse is 0.3mJ, in which case the spacing has a default value of 14 μm, asdetermined by the bubble size for that level of energy at thatparticular wavelength. These parameters are relevant to cornealprocedures; appropriate laser parameters must be selected for alternateophthalmic procedures, such as operations on the lens, for which thehardware of present invention can also be suitably modified.

The surgeon can thus use the information provided in the various windowsto provide diagnostic information of the actual condition of the targettissue to the surgeon/user. Thus, the surgeon might first establish thepattern in the screen in plane view, observe the results of hisselection in various perspective views, as shown in FIGS. 12 and 14,wherein the proposed lesion is automatically indicated, and reflect uponthe likely outcome of the surgery with the ability to edit, an alter asdesired, the designated template pattern prior to initiating theprocedure.

At any point during the diagnostics and the lesion selection phase, theuser can superpose the actual laser aim points on the proposed lesionshapes and/or image of the tissue (from the video camera) indicated onthe screen through a click of the mouse, on the “show aim points” optionfrom, e.g., the “treatment” module, box 37 in FIG. 13. This option isalso activated just prior to the final step in the procedure, whichinvolves actual firing of the laser to perform the surgery, as indicatedby block 144 in FIG. 11.

The template-controlled laser firing must occur precisely in accordancewith the pre-selected targeting sequence. It is the tracking system(including diagnostic, tracking and mirror movement) which is thecritical link in this feedback loop. This function is indicated by block134 in FIG. 11. The tracking feature is automatically activated duringdiagnostic and treatment phases. As noted earlier in this disclosure, ifthe tracking subsystem fails to move the servo controlled turningmirrors to maintain the target within acceptable error tolerances, thenthe template-controlled laser firing will be disabled until the imagesare again reacquired or until the surgeon re-initiates the program.Likewise, if an obstruction (such as a blinking eyelid for ophthalmicprocedures or transient debris in industrial procedures) were tointerfere with the imaging/tracking light path (which also correspondswith the laser beam path), the template-controlled laser firing will beinterrupted until the images are reacquired and the appropriate positionin the template firing sequence is recovered. The closed loop 135indicates automatic aim point maintenance for the laser. If allconditions are met (patient ready, tracking is online, laser is armed),the surgeon may select the “start” option under the “treatment” module37 (see FIG. 13) which commences the surgery. If, at any time loss oftracking is indicated, or other, potentially unsafe conditions areencountered (such as energy deviation, per, e.g., block 136 in FIG. 11),the firing sequence is automatically immobilized through safetyinterlock features shown as block 100 in FIG. 11 (see also FIG. 10). Thesurgeon can also choose to interrupt the procedure manually by pressingon the fire control or, abort switch 24, also connected to the safetyinterlock system. In either case, the last aim point position is storedin the computer memory, along with all other pertinent data concerningthe operation. The procedure can therefore be resumed at will byclicking a “continue” option (also shown in box 37 of FIG. 13). This hasthe effect of allowing the target area to be reacquired and tracked, andthe laser will then fire according to the original pattern and sequenceselected, starting at the precise aim point location last exercisedprior to the interruption.

Upon completion of the operation, a “report” option (see, e.g., box 37in FIG. 13) may be provided, whereby the procedure details can besummarized and pertinent statistical information stored and displayed. A“statistical” module (not shown) may be provided as part of the software(e.g., under the “file” module) to fulfill this function.Characteristics of the treatment which may be recorded and reported mayinclude the total number of laser pulses fired, the total energydeposited into the tissue, time elapsed and other pertinent data.

A disc file input/output (I/O) module is also incorporated to supportall the necessary exchanges with external memory devices. Thus all theinformation about a given surgical session can be stored for futureanalysis and/or reports, along with the values selected for allparameters, templates, and personal data. The results of theprofilometric measurements can be stored in a separate file, which maybe retrieved when needed.

Note that the techniques for obtaining mapping and profile informationof selected surfaces within the eye in the embodiments of the presentinvention are not limited to any one specific surface. The techniquesdescribed herein apply to either the cornea or the iris, lens, etc. Withsome modification in the imaging optics, retinal procedures may beincluded as well (note that the retina is a reflecting surface in thatthere is an index of refraction change across the surface. Consequently,there will be for each incident light ray a reflected ray, a refractedray, ray absorption, and scattering of light, all of which must be takeninto account when selecting specific methods for acquiring andinterpreting data).

It should also be understood that the system of the invention is usefulto the surgeon as a diagnostic and analytical tool, aside from its usesin actual surgery. The system provides for the doctor highly stabilizedimages of the patient's tissue—particularly the ocular tissue—notachievable with instruments prior to this invention. The doctor is givena display of the tissues, along with simultaneous tracking andstabilization. The invention therefore gives the doctor a very importanttool in analysis and diagnosis of a patient's condition, and theinvention should be understood to encompass the system as described evenwithout the surgical laser beam itself. The system, with itscomputer-generated images (CGIs) on the display screen as well as directvideo microscopic images displays of the patient/target, gives thedoctor a means of visualizing the eye condition, as a replacement forthe doctor's directly looking at the target tissues. TheTemplate-Controlled Surgical Laser (or, Ophthalmic Surgical Workstation)invention should be considered as including the user interface, thecomputer and memory storage device relative to creating, modifying,storing, and executing surgical template programs. This assembly isdefined in greater detail by Sklar in U.S. patent application No.475,657 (now abandoned) which is incorporated herein by reference.

The above described preferred embodiments are intended to illustrate theprinciples of the invention but without limiting its scope. Otherembodiments and variations to these preferred embodiments will beapparent to those skilled in the art and may be made without departingfrom the essence and scope of the invention as defined in the claims.

1. A laser system for ablating a surface of a cornea of an eye to changea refractive power of the eye, the system comprising: a pulsed laser formaking a first light beam of a pulsed ablative laser light energy; anenergy detector monitoring the energy of the pulsed beam of the ablativelight energy; a slit lamp illuminator illuminating the cornea with asecond light beam; a surgical microscope viewing light from the secondbeam reflected from the cornea; and a processor comprising a memory anda program, the processor controlling of a firing of the laser accordingto a predetermined sequence of automatic motion instructions, thecontrol of the laser firing including an interruption of the firing ofthe laser in response to a first condition signal and a continuation ofthe laser firing according to the predetermined sequence in response toa second condition signal.
 2. The system of claim 1 further wherein theslit lamp is mounted at a fixed location relative to a camera.
 3. Thesystem of claim 2 wherein the slit lamp and the camera are arranged tocollect corneal information over a region of the cornea, the region ofthe cornea extending to a limbus of the cornea.
 4. The system of claim 3wherein the camera is a video camera.
 5. The system of claim 4 furtherwherein a structure of the slit lamp is rotatable around a central axisto collect global corneal data.
 6. The system of claim 1 wherein theslit lamp is arranged for measuring a thickness of the cornea from aslit lamp image.
 7. The system of claim 6 wherein the slit lamp imagecomprises a video image.
 8. The system of claim 7 wherein the videoimage comprises a digitized video image.
 9. The system of claim 8wherein the processor determines local radii of curvature of the corneafrom the digitized video image.
 10. The system of claim 1 wherein theilluminator comprises an off axis slit lamp illuminator.
 11. The systemof claim 10 further comprising a video display visible to a user of thesystem and electronically coupled to the processor, the video displayshowing a menu of selections to the user.
 12. The system of claim 11wherein the menu of selections comprises a plurality of user selectablesymbols.
 13. The system of claim 12 wherein the slit lamp illuminatorcomprises an illuminator for obtaining a thickness of the cornea. 14.The system of claim 12 wherein the laser firing is initiated in responseto an action of the user.
 15. The system of claim 12 wherein thesequence is predetermined by a user prior to treating the patient. 16.The system of claim 12 wherein the interruption comprises a manualinterruption and the first condition signal is a result of an action ofthe user.
 17. The system of claim 12 wherein the pulsed laser comprisesan excimer laser.
 18. The system of claim 12 wherein a wavelength of thelight energy of the laser comprises a non-visible wavelength.
 19. Thesystem of claim 12 further comprising: optical path means for receivingthe short pulse laser beam and for aiming the beam at a point in X-Ydirections and focussing the beam at a depth as desired toward a target,including a front lens element from which the beam exits the opticalpath means toward the patient, beam steering means connected to theoptical path means for controlling the position at which the beam isaimed in X-Y directions, beam focussing means connected to the opticalpath means for controlling the depth at which the laser beam isfocussed, tracking means for tracking eye movements of the patientduring the progress of the surgery, including X-Y tracking means fortracking a feature of the eye in X and Y directions, and depth or Ztracking means for tracking depth movements of the eye's feature, towardand away from the workstation, and safety interrupt means associatedwith the processor for interrupting delivery of the laser beam to thepatient when it is determined via the processor that the tracking meanshas lost the feature being tracked.
 20. The system of claim 12 whereinthe interruption comprises an automatic interruption and the firstcondition signal comprises a response to at least one operationalspecification not being met.
 21. The system of claim 20 wherein at leastone operational specification comprises a measured laser energy.
 22. Thesystem of claim 21 wherein a fraction of the beam passes through areflecting surface for measuring the laser pulse energy.
 23. The systemof claim 20 further comprising a sensor for generating an electricalsignal for measuring a position of the eye, and at least one operationalspecification comprises measuring the position of the eye.
 24. Thesystem of claim 12 wherein a last position of the sequence is stored inthe processor during the interruption.
 25. The system of claim 24wherein the predetermined sequence of automatic motion instructionscontrols a position of the beam of energy on the surface of the cornea.26. The system of claim 25 wherein the sequence of motion instructionscorresponds to a pattern of pulses of the laser beam delivered to thesurface of the cornea.
 27. The system of claim 26 wherein the laststored position of the sequence corresponds to a location of the laserbeam.
 28. A method for ablating a surface of a cornea of an eye tochange a refractive power of the eye, the method comprising: making afirst beam of a pulsed ablative laser light energy with a pulsed laser;monitoring the energy of the pulsed beam of the ablative light energywith an energy detector; illuminating the cornea with a second beam oflight from a slit lamp illuminator; viewing light of the first beamreflected from the cornea with a surgical microscope; and controlling afiring of the laser with a processor comprising a memory and a programadapted to fire the laser according to a predetermined sequence ofautomatic motion instructions, the controlling of the laser firingincluding interrupting the firing of the laser in response to a firstcondition signal and continuing the laser firing according to thepredetermined sequence in response to a second condition signal.
 29. Themethod of claim 28 wherein the beam of the slit lamp illuminatorcomprises a ribbon-shaped illuminating light beam.
 30. The method ofclaim 28 further comprising measuring a thickness of the cornea from aslit lamp image.
 31. The method of claim 30 wherein the slit lamp imagecomprises a video image.
 32. The method of claim 31 wherein the videoimage comprises a digitized video image.
 33. The method of claim 32further comprising measuring local radii of curvature of the cornea fromthe digitized video image.
 34. The method of claim 28 further comprisingmounting the slit lamp at a fixed location relative to a camera.
 35. Themethod of claim 34 wherein the slit lamp and the camera are arranged tocollect corneal information over a region of the cornea, the region ofthe cornea extending to a limbus of the cornea.
 36. The method of claim35 wherein the camera is a video camera.
 37. The method of claim 36further comprising rotating a structure of the slit lamp around acentral axis to collect global corneal data.
 38. The method of claim 28wherein the illuminator comprises an off axis slit lamp illuminator. 39.The method of claim 38 further comprising showing a menu of selectionsto a user on a video display, the video display being visible to a userof the system and electronically coupled to the processor.
 40. Themethod of claim 39 wherein the menu of selections comprises a pluralityof user selectable symbols.
 41. The method of claim 40 wherein thefiring of the laser is initiated in response to an action of a user. 42.The method of claim 40 wherein the sequence is predetermined in responseto an action of a user prior to treating the patient.
 43. The method ofclaim 40 wherein the interruption comprises a manual interruption andthe first condition signal comprises a response to an action of a user.44. The method of claim 40 wherein the pulsed laser comprises an excimerlaser.
 45. The method of claim 40 wherein a wavelength of the lightenergy of the laser comprises a non-visible wavelength.
 46. The methodof claim 40 further comprising: receiving the short pulse laser beam andaiming the beam at a point in X-Y directions and focussing the beam at adepth with an optical means and when appropriate toward a target,through a front lens element, controlling the position at which the beamis aimed in X-Y directions, using a beam steering means connected to theoptical means, controlling the depth at which the laser beam isfocussed, with a beam focussing means connected to the optical means,tracking eye movements of the patient during the progress of thesurgery, in X and Y directions, with an X-Y tracking means for trackinga feature of the eye, and as to depth movements of the eye with a depthor Z tracking means, automatically shifting the optical path means asthe feature of the eye is tracked through X-Y and Z movements, so as tochange the aim and focus of the laser beam when necessary to follow suchmovements of the eye, with the aid of the processor connected to thetracking means, and automatically interrupting delivery of the laserbeam to the patient when it is determined via the microprocessor thatthe tracking means has lost the feature being tracked.
 47. The method ofclaim 40 wherein the interruption comprises an automatic interruptionand the first condition signal comprises a response to at least oneoperational specification not being met.
 48. The method of claim 47further comprising measuring a position of the eye with a sensorgenerating an electrical signal, and at least one operationalspecification comprises measuring the position of the eye.
 49. Themethod of claim 47 wherein at least one operational specificationcomprises a measured laser energy.
 50. The method of claim 49 wherein afraction of the first light beam passes through a reflecting surface formeasuring the laser energy.
 51. The method of claim 40 wherein a lastposition in the interrupted sequence is stored by the processor.
 52. Themethod of claim 51 wherein the predetermined sequence of automaticmotion instructions controls a position of the beam of energy on thesurface of the cornea.
 53. The method of claim 52 wherein the sequenceof motion instructions corresponds to a pattern of pulses of the laserbeam delivered to the surface of the cornea.
 54. The method of claim 53wherein the stored last position of the sequence corresponds to alocation of the laser beam.